Description　
Microwave ablation (MWA) is a technique to destroy tumors and soft tissue using microwave energy to create thermal coagulation and localized tissue necrosis. MWA is used to treat tumors not amenable to resection and to treat patients ineligible for surgery due to age, comorbidities, or poor general health. MWA may be performed as an open procedure, laparoscopically, percutaneously, or thoracoscopically under image guidance (e.g., ultrasound, computed tomography, magnetic resonance imaging) with sedation, or local or general anesthesia. This technique is also referred to as microwave coagulation therapy.

For individuals who have unresectable primary or metastatic breast cancer who receive MWA, the evidence includes case series and a systematic review of feasibility and pilot studies conducted prior to 2010. The evidence is insufficient to determine the effects of the technology on health outcomes.

For individuals who have an unresectable primary or metastatic hepatic tumor who receive MWA, the evidence includes randomized controlled trials (RCTs), comparative observational studies, case series, and systematic reviews comparing MWA to radiofrequency ablation (RFA) and to surgical resection. The relevant outcomes are overall survival (OS), disease-specific survival, symptoms, quality of life, and treatment-related mortality and morbidity. The body of evidence indicates that MWA is an effective option in patients for whom resection is not an option. Although studies had methodological limitations, they consistently showed that that MWA and RFA had similar survival outcomes with up to five years of follow-up in patients with a single tumor ≤ 5 cm or up to three nodules ≤ 3 cm each. In meta-analyses of observational studies, patients receiving MWA had higher local recurrence rates and lower survival than those who received resection, but the patient populations were not limited to those who had unresectable tumors. MWA was associated with lower complications, intraoperative blood loss, and hospital length of stay. The evidence is sufficient to determine the effects of the technology on health outcomes.

For individuals who have an unresectable primary or metastatic lung tumor who receive MWA, the evidence includes one RCT, retrospective observational studies, and systematic reviews of these studies. The relevant outcomes are OS, disease-specific survival, symptoms, quality of life, and treatment-related mortality and morbidity. The body of evidence indicates that MWA is an effective option in patients for whom resection is not an option. In the RCT, direct comparison of MWA and RFA in patients with primary or metastatic lung cancer (mean tumor size 1.90 cm [± 0.89] at baseline) found similar mortality rates up to 12 months of follow-up. In the first of three systematic reviews that included 12 retrospective observational studies, local recurrence rates were similar for MWA and RFA at a range of 9 to 47 months of follow-up. In the second systematic review with a meta-analysis, there was lower OS with MWA compared to RFA but studies were not directly comparable due to clinical and methodological heterogeneity. However, the authors concluded that percutaneous RFA and MWA were both effective with a high safety profile. In the third systematic review using a network meta-analysis, the weighted average OS rates for MWA were 82.5%, 54.6%, 35.7% 29.6%, and 16.6% at 1, 2, 3, 4, and 5 years, respectively. Limitations of the body of evidence included a lack of controlled studies and heterogeneity across studies. The RCT did not report results by tumor size or the number of metastases. The observational studies included in the systematic reviews did not report sufficient information to assess the effectiveness or safety of MWA in subgroups based on the presence of multiple tumors or total tumor burden. Therefore, conclusions about the evidence sufficiency can only be made about patients with single tumors. For this population, the evidence is sufficient to determine the effects of the technology on health outcomes.

For individuals who have an unresectable primary or metastatic renal tumor who receive MWA, the evidence includes one RCT that compared MWA to partial nephrectomy and case series. The relevant outcomes are OS, disease-specific survival, symptoms, quality of life, and treatment-related mortality and morbidity. In the RCT, overall local recurrence-free survival at 3 years was 91.3% for MWA and 96.0% for partial nephrectomy (p = 0.54). This positive outcome should be replicated in additional RCTs. There are also no controlled studies comparing MWA to other ablation techniques in patients with renal tumors. The evidence is insufficient to determine the effects of the technology on health outcomes.

For individuals who have unresectable primary or metastatic solid tumors other than breast, hepatic, lung, or renal who receive MWA, the evidence includes case series. The evidence is insufficient to determine the effects of the technology on health outcomes.

Background 
MICROWAVE ABLATION
Microwave ablation (MWA) is a technique that uses microwave energy to induce an ultra-high speed, 915 MHz or 2.450 MHz (2.45 GHz), alternating electric field, which causes water molecule rotation and creates heat. This results in thermal coagulation and localized tissue necrosis. In MWA, a single microwave antenna or multiple antennas connected to a generator are inserted directly into the tumor or tissue to be ablated; energy from the antennas generates friction and heat. The local heat coagulates the tissue adjacent to the probe, resulting in a small, 2- to 3-cm elliptical area (5 x 3 cm) of tissue ablation. In tumors greater than 2 cm in diameter, 2 to 3 antennas may be used simultaneously to increase the targeted area of MWA and shorten operative time. Multiple antennas may also be used simultaneously to ablate multiple tumors. Tissue ablation occurs quickly, within 1 minute after a pulse of energy, and multiple pulses may be delivered within a treatment session, depending on tumor size. The cells killed by MWA are typically not removed but are gradually replaced by fibrosis and scar tissue. If there is local recurrence, it occurs at the margins. Treatment may be repeated as needed. MWA may be used for the following purposes: (1) to control local tumor growth and prevent recurrence; (2) to palliate symptoms; and (3) to extend survival duration.

MWA is similar to radiofrequency (RFA) and cryosurgical ablation. However, MWA has potential advantages over RFA and cryosurgical ablation. In MWA, the heating process is active, which produces higher temperatures than the passive heating of RFA and should allow for more complete thermal ablation in less time. The higher temperatures reached with MWA ( > 100 C) can overcome the "heat sink" effect in which tissue cooling occurs from nearby blood flow in large vessels, potentially resulting in incomplete tumor ablation. MWA does not rely on the conduction of electricity for heating and, therefore, does not flow electrical current through patients and does not require grounding pads, because there is no risk of skin burns. Additionally, MWA does not produce electric noise, which allows ultrasound guidance during the procedure without interference, unlike RFA. Finally, MWA can take less time than RFA, because multiple antennas can be used simultaneously.

Adverse Events
Complications from MWA are usually mild and may include pain and fever. Other complications associated with MWA include those caused by heat damage to normal tissue adjacent to the tumor (e.g., intestinal damage during MWA of the kidney or liver), structural damage along the probe track (e.g., pneumothorax as a consequence of procedures on the lung), liver enzyme elevation, liver abscess, ascites, pleural effusion, diaphragm injury, or secondary tumors if cells seed during probe removal. MWA should be avoided in pregnant women because potential risks to the patient and/or fetus have not been established, and in patients with implanted electronic devices (e.g., implantable pacemakers) that may be adversely affected by microwave power output.

Applications
MWA was first used percutaneously in 1986 as an adjunct to liver biopsy. Since then, MWA has been used to ablate tumors and tissue to treat many conditions including hepatocellular carcinoma, breast cancer, colorectal cancer metastatic to the liver, renal cell carcinoma, renal hamartoma, adrenal malignant carcinoma, non-small-cell lung cancer, intrahepatic primary cholangiocarcinoma, secondary splenomegaly and hypersplenism, abdominal tumors, and other tumors not amenable to resection. Well-established local or systemic treatment alternatives are available for each of these malignancies. The potential advantages of MWA for these cancers include improved local control and other advantages common to any minimally invasive procedure (e.g., preserving normal organ tissue, decreasing morbidity, shortening length of hospitalization). MWA also has been investigated as a treatment for unresectable hepatic tumors, as both primary and palliative treatment, and as a bridge to liver transplant. In the latter setting, MWA is being assessed to determine whether it can reduce the incidence of tumor progression while awaiting transplantation and thus maintain a patient’s candidacy while awaiting liver transplant.

Regulatory Status
Multiple MWA devices have been cleared for marketing by the U.S. Food and Drug Administration (FDA) through the 510(k) process. These devices are indicated for soft tissue ablation, including partial or complete ablation of nonresectable liver tumors. Some devices are specifically cleared for use in open surgical ablation, percutaneous ablation, or laparoscopic procedures. Table 1 is a summary of selected MWA devices cleared by the FDA.

The FDA used determinations of substantial equivalence to existing radiofrequency and MWA devices to clear these devices. FDA product code: NEY.

This evidence review does not address MWA for the treatment of splenomegaly or ulcers, for cardiac applications, or as a surgical coagulation tool.

Table 1. Selected Microwave Ablation Devices Cleared by FDA

FDA: U.S. Food and Drug Administration.

Related Policies
70175 Cryosurgical Ablation of Primary or Metastatic Liver Tumors
70191 Radiofrequency Ablation of Primary or Metastatic Liver Tumors
70192 Cryosurgical Ablation of Miscellaneous Solid Tumors Other Than Liver, Prostate, or Dermatologic Tumors
70195 Radiofrequency Ablation of Miscellaneous Solid Tumors Excluding Liver Tumors
80111 Transcatheter Arterial Chemoembolization (TACE) to Treat Primary or Metastatic Liver Malignancies
80143 Radioembolization for Primary and Metastatic Tumors of the Liver

Policy
Microwave ablation of primary or metastatic hepatic tumors may be considered MEDICALLY NECESSARY under the following conditions:

• The tumor is unresectable due to location of lesion[s] and/or comorbid conditions.
• A single tumor of ≤ 5 cm or up to 3 nodules ≤ 3 cm each.

Microwave ablation of primary or metastatic lung tumors may be considered MEDICALLY NECESSARY under the following conditions:

• The tumor is unresectable due to location of lesion and/or comorbid conditions.
• A single tumor of ≤ 3 cm.

Microwave ablation of more than a single primary or metastatic tumor in the lung is considered investigational/unproven and therefore NOT MEDICALLY NECESSARY.

Microwave ablation of primary or metastatic tumors other than liver or lung is considered investigational/unproven and therefore NOT MEDICALLY NECESSARY. 

Policy Guidelines 
Coding

Please see the Codes table for details.

Benefit Application
BlueCard^®/National Account Issues
State or federal mandates (e.g., FEP) may dictate that all U.S. Food and Drug Administration (FDA)-approved devices, drugs, or biologics may not be considered investigational, and thus use of these devices may be assessed only on the basis of their medical necessity.

Rationale
The evidence review was created in December 2011 and has been updated regularly with searches of the PubMed database. The most recent literature update was performed through Aug. 30, 2022.

Evidence reviews assess the clinical evidence to determine whether the use of technology improves the net health outcome. Broadly defined, health outcomes are the length of life, quality of life (QOL), and ability to function including benefits and harms. Every clinical condition has specific outcomes that are important to patients and to managing the course of that condition. Validated outcome measures are necessary to ascertain whether a condition improves or worsens; and whether the magnitude of that change is clinically significant. The net health outcome is a balance of benefits and harms.

To assess whether the evidence is sufficient to draw conclusions about the net health outcome of a technology, 2 domains are examined: the relevance and the quality and credibility. To be relevant, studies must represent 1 or more intended clinical use of the technology in the intended population and compare an effective and appropriate alternative at a comparable intensity. For some conditions, the alternative will be supportive care or surveillance. The quality and credibility of the evidence depend on study design and conduct, minimizing bias and confounding that can generate incorrect findings. The randomized controlled trial (RCT) is preferred to assess efficacy; however, in some circumstances, nonrandomized studies may be adequate. Randomized controlled trials are rarely large enough or long enough to capture less common adverse events and long-term effects. Other types of studies can be used for these purposes and to assess generalizability to broader clinical populations and settings of clinical practice.

Unresectable Primary or Metastatic Solid Organ Tumors
Clinical Context and Therapy Purpose
The purpose of microwave ablation (MWA) in patients who have unresectable primary or metastatic solid organ tumors is to provide a treatment option that is an alternative to or an improvement on existing therapies.

The question addressed in this evidence review is: Does the use of MWA improve the net health outcome in individuals with unresectable solid organ primary or metastatic tumors?

The following PICO was used to select literature to inform this review.

Populations
The relevant population of interest is those with unresectable primary or metastatic hepatic, lung, renal, and solid tumors other than hepatic, lung, or renal. In patients with disseminated disease or in cases where age or comorbidity precludes a surgical approach, volume reduction, symptom relief, and palliation may be appropriate. In select patients with small tumors, ablation techniques may provide a minimally invasive alternative to surgery.

Interventions
The therapy being considered is MWA.

Comparators
The following therapies are currently being used to manage unresectable primary or metastatic hepatic, lung, or renal tumors: radiofrequency ablation (RFA).

Transcatheter arterial chemoembolization (TACE) may be used in the management of unresectable primary or metastatic hepatic tumors. Cryoablation may be used in the management of unresectable primary or metastatic renal and lung tumors.

The following therapies are currently being used to manage other unresectable primary or metastatic solid tumors: standard of care, which may include systemic therapy, radiotherapy, and/or select local ablation therapies.

Outcomes
The general outcomes of interest are overall survival (OS), disease-specific survival, symptoms, QOL, and treatment-related mortality and morbidity.

Treatment-related morbidities may vary by tumor type. For example, treatment for lung cancer may lead to pneumothorax. Follow-up for treatment-related morbidity is months post procedure. Follow-up to monitor for OS and recurrence rates may be measured in years of follow-up.

Study Selection Criteria
Methodologically credible studies were selected using the following principles:

• To assess efficacy outcomes, comparative controlled prospective trials were sought, with a preference for RCTs and systematic reviews of these studies.
• In the absence of such trials, comparative observational studies were sought, with a preference for prospective studies.
• To assess long-term outcomes and adverse events, single-arm studies that capture longer periods of follow-up and/or larger populations were sought.
• Studies with duplicative or overlapping populations were excluded.

Unresectable Primary or Metastatic Hepatic Tumors
Review of Evidence
Systematic Reviews
Several systematic reviews have evaluated MWA for patients with liver tumors.^1,2,3,4,5 The 4 most recent, published in 2016,¹ 2019,⁴ 2020,⁵ and 2022⁶ are summarized in Tables 2 through 4. Two of these reviews compared MWA to RFA,^6,1,1 compared MWA to resection,⁴ and 1 compared MWA to a variety of therapies, including RFA and resection.⁵

Table 2. Microwave Ablation for Hepatic Tumors: Comparison of Trials/Studies Included in SR and MA

Table 3. Microwave Ablation for Hepatic Tumors: SR and MA Characteristics

HCC: hepatocellular carcinoma; MA: meta-analysis; MWA: microwave ablation; RCT: randomized controlled trial; RFA: radiofrequency ablation; SR: systematic review.

Table 4. Microwave Ablation for Hepatic Tumors: SR and MA Results

CI: confidence interval; MA: meta-analysis; MWA: microwave ablation; N: sample size; NR: not reported; RFA: radiofrequency ablation; SR: systematic review.

Chinnaratha et al. (2016) published a systematic review of RCTs and observational studies that compared the effectiveness and safety of RFA with MWA in patients who had primary hepatocellular carcinoma (HCC).¹ PubMed, EMBASE, and Cochrane Central databases were searched between 1980 and 2014 for human studies comparing the 2 technologies. The primary outcome was the risk of local tumor progression; secondary outcomes were complete ablation, OS, and major adverse events. Odds ratios were combined across studies using a random-effects model. Ten studies (1 RCT8, 1 prospective cohort, 8 retrospective) were included. One study was conducted in Australia and the others in China or Japan. Using the modified Newcastle-Ottawa quality assessment scale, the reviewers rated 5 of 10 studies high quality. The overall local tumor progression rate was 14% (176/1298). There was no difference in local tumor progression rates between RFA and MWA (odds ratio [OR], 1.01; 95% confidence interval [CI], 0.67 to 1.50; p = .98). The complete ablation rate, 1- and 3- year OS, and major adverse events were similar between the 2 modalities (p > .05 for all). Subgroup analysis showed local tumor progression rates were lower with MWA for treatment of larger tumors ( OR, 1.88; 95% CI, 1.10 to 3.23; p = .02). No significant publication bias was detected nor was interstudy heterogeneity (I2 < 50%, p > .1) observed for any measured outcomes. The reviewers concluded that both MWA and RFA are effective and safe.

Glassberg et al. (2019) conducted a systematic review of MWA compared to resection in patients with HCC or metastatic liver cancer. One RCT (Xu et al. [2015] ²⁹) was included; the other studies (n = 15) were observational (2 prospective, 13 retrospective). Patients who received MWA had a significantly higher risk of local tumor progression compared to those who received resection (relative risk [RR] , 3.04; p < .001). At 1 year, OS did not differ between MWA and resection but 3- and 5-year OS was significantly higher in patients who had received resection. Overall and major complications were lower with MWA compared to resection. Additionally, operative time, intraoperative blood loss, and hospital length of stay were significantly lower with MWA. Some studies included patients that were nonresectable in the MWA treatment arm, but due to limited reporting and patient preference affecting which treatment was performed, the reviewers were not able to calculate the number of patients who were nonresectable or to conduct subgroup analyses by resectable versus unresectable tumors. Microwave ablation was typically selected for patients with smaller and/or deeper tumors, more comorbidities, and a preference for a less invasive procedure. The reviewers concluded that MWA can be an effective and safe alternative to hepatic resection in patients or tumors that are not amenable to resection, but more studies are needed to determine the target population that would benefit most from MWA.

Cui et al. (2020) conducted a systematic review and meta-analysis of MWA compared to various treatment modalities. The analysis included 4 RCTs, with 3 comparing MWA to RFA^37,8,23 and 1 comparing MWA to TACE.²⁷ The remaining 11 studies were nonrandomized trials comparing MWA to RFA (n = 8 studies), resection (n = 2 studies), or ethanol ablation (n = 1 study). Meta-analyses were not performed for MWA versus TACE or ethanol ablation, because these comparisons were only examined in 1 study each. Meta-analyses of studies comparing MWA to RFA found no difference in 3-year OS, 5-year OS, local tumor progression at 1 year, progression-free survival at 3 years, or major complications. A meta-analysis of 2 nonrandomized studies comparing MWA to resection found no difference in 3-year OS between treatments; however, this comparison is limited by the small number of studies and lack of RCTs included. The reviewers concluded that MWA showed similar safety and efficacy compared with RFA, but higher quality clinical studies are needed to validate the superiority of MWA.

Dou et al. (2022) conducted a systematic review and meta-analysis that compared the safety and efficacy of MWA compared to RFA in patients with HCC.⁶ The analysis included 28 cohort studies and 5 RCTs. Overall, there was no significant difference in disease-free survival, OS, or major complications between the 2 groups. In the cohort studies, MWA had a lower local tumor progression rate than RFA (OR, 0.78; 95% CI, 0.64 to 0.96; p = .02). The reviewers concluded that there were various differences in the included studies (e.g., equipment used, operator experience) and that more high-quality RCTs are needed to draw a definitive conclusion on the pros versus cons of MWA and RFA in this patient population.

Randomized Controlled Trials
Five RCTs have compared MWA to RFA in patients with primary hepatic tumors^{58,8,37,23,60}, and 1 RCT has compared MWA to resection.²⁹ The majority of these trials were included in the systematic reviews and meta-analyses described above and are not discussed in further detail here. Tables 5 and 6 summarize the characteristics and results of trials comparing MWA to RFA that have not been included in systematic reviews or meta-analyses. Tables 9 and 10 summarize the relevance, design, and conduct limitations of these trials.

An RCT by Vietti Violi et al. (2018) compared the effectiveness of RFA and MWA in treating inoperable HCC in 152 patients with up to 3 lesions of 4 cm or smaller.⁵⁸ At 2 years, 6% (6/98) of lesions treated with MWA had local tumor progression versus 12% (12/104) of lesions treated with RFA ( RR, 1.62; 95% CI , 0.66 to 3.94; p = .27). Few complications and no treatment-related deaths were reported for either group. Overall survival at 2 years was not significantly different between the groups. Because some patients did not receive the allocated treatment or were lost to follow-up, the analyses were per protocol rather than intention to treat. In addition, the investigators had planned to assess the effects of the treatments on larger lesions, but only a few patients had lesions of nearly 4 cm, making a detailed analysis impossible. A 5-year follow-up is planned for this study.

Chong et al. (2020) conducted a RCT comparing MWA to RFA in 93 patients with HCC (up to 3 lesions of 5 cm or smaller).⁶⁰ Mean tumor size was 3.1 cm in the MWA group and 2.8 cm in the RFA group. The primary outcome of this study was the rate of complete ablation at 1 month, which did not differ significantly for MWA (95.7%) versus RFA (97.8%; p > .99). Rates of OS up to 5 years and rates of disease-free survival up to 3 years were similar between groups. However, the sample size calculations were based on rates of complete ablation at 1 month, so the study may not have been adequately powered to detect differences in OS or disease-free survival.

Table 5. MWA versus RFA in Patients with Hepatic Tumors: Summary of Key RCT Characteristics

Table 6. MWA versus RFA in Patients with Hepatic Tumors: Summary of Key RCT Results

CI: confidence interval; MWA: microwave ablation; NR: not reported; RCT: randomized controlled trial; RFA: radiofrequency ablation.
 
Zaitoun et al. (2021) compared the safety and efficacy of combination therapy with TACE and MWA (n = 89) compared to TACE (n = 84) or MWA (n = 92) only in patients with solitary HCC lesions measuring between 3 to 5 cm.⁶¹ TACE was performed first, followed by MWA after 15 days. Mean tumor size was 3.6 cm, 3.9 cm, and 3.7 cm in the TACE, MWA, and combination groups, respectively (p = .053). Complete response at 1 month was achieved by 86.5% of patients who received combination therapy compared with 54.8% of patients treated with TACE and 56.5% of patients treated with MWA. Patients treated with combination therapy had a significantly lower recurrence rate at 12 months (p = .0001) and a significantly higher OS rate at 3 years (69.6%; p = .02). Post-procedural minor adverse events (e.g., nausea, vomiting, abdominal pain, and low-grade fever) were reported in 24.7%, 47.6%, and 38% of patients in the combined, TACE, and MWA groups, respectively. Severe hepatic dysfunction was observed in 1 patient in the combined group and 3 patients in the TACE group. Tumor seeding was reported in 2 patients in the MWA group. A decrease in alpha-fetoprotein (AFP) concentration was observed in 75%, 63%, and 48% of patients who underwent combined therapy, MWA, or TACE, respectively. Study characteristics and results are summarized in Tables 7 and 8. Study relevance, design, and conduct limitations are summarized in Tables 9 and 10.

Table 7. MWA versus TACE in Patients with Hepatic Tumors: Summary of Key RCT Characteristics

HCC: hepatocellular carcinoma; MWA: microwave ablation; RCT: randomized controlled trial; TACE: transarterial chemoembolization.

Table 8. MWA versus TACE in Patients with Hepatic Tumors: Summary of Key RCT Results

CR: complete response; MWA: microwave ablation; PD: progressive disease; PR: partial response; RCT: randomized controlled trial; SD: stable disease; TACE: transarterial chemoembolization.
^a Treatment response based on mRECIST criteria.

Table 9. Study Relevance Limitations

The study limitations stated in this table are those notable in the current review; this is not a comprehensive gaps assessment.
^a Population key: 1. Intended use population unclear; 2. Clinical context is unclear; 3. Study population is unclear; 4. Study population not representative of intended use.
^b Intervention key: 1. Not clearly defined; 2. Version used unclear; 3. Delivery not similar intensity as comparator; 4. Not the intervention of interest.
^c Comparator key: 1. Not clearly defined; 2. Not standard or optimal; 3. Delivery not similar intensity as intervention; 4. Not delivered effectively.
^d Outcomes key: 1. Key health outcomes not addressed; 2. Physiologic measures, not validated surrogates; 3. No CONSORT reporting of harms; 4. Not established and validated measurements; 5. Clinical significant difference not prespecified; 6. Clinical significant difference not supported.
^e Follow-Up key: 1. Not sufficient duration for benefit; 2. Not sufficient duration for harms.

Table 10. Study Design and Conduct Limitations

The study limitations stated in this table are those notable in the current review; this is not a comprehensive gaps assessment.
^a Allocation key: 1. Participants not randomly allocated; 2. Allocation not concealed; 3. Allocation concealment unclear; 4. Inadequate control for selection bias.
^b Blinding key: 1. Not blinded to treatment assignment; 2. Not blinded outcome assessment; 3. Outcome assessed by treating physician.
^c Selective Reporting key: 1. Not registered; 2. Evidence of selective reporting; 3. Evidence of selective publication.
^d Data Completeness key: 1. High loss to follow-up or missing data; 2. Inadequate handling of missing data; 3. High number of crossovers; 4. Inadequate handling of crossovers; 5. Inappropriate exclusions; 6. Not intent to treat analysis (per protocol for noninferiority trials).
^e Power key: 1. Power calculations not reported; 2. Power not calculated for primary outcome; 3. Power not based on clinically important difference.
^f Statistical key: 1. Analysis is not appropriate for outcome type: (a) continuous; (b) binary; (c) time to event; 2. Analysis is not appropriate for multiple observations per patient; 3. Confidence intervals and/or p values not reported; 4. Comparative treatment effects not calculated.

Hepatic Metastases From Primary Cancers From Other Sites
Systematic Reviews
A Health Technology Assessment by Loveman et al. (2014)⁶² and a Cochrane review by Bala et al. (2013)⁶³ reported on ablation for liver metastasis. Reviewers found insufficient evidence to determine any benefits of MWA for liver metastasis over surgical resection.

Pathak et al. (2011) conducted a systematic review of ablation techniques for colorectal liver metastases, which included 13 studies on MWA (N = 406 patients) with a minimum of 1-year follow-up.⁶⁴ Mean survival rates were 73%, 30%, and 16% and ranged from 40% to 91.4%, 0% to 57%, and 14% to 32% at the 1-, 3-, and 5-year follow-ups, respectively. Minor and major complication rates were considered acceptable and ranged from 6.7% to 90.5% and 0% to 19%, respectively. Local recurrence rates ranged from 2% to 14%.

Mimmo et al. (2022) conducted a systematic review of MWA for colorectal liver metastases.⁶⁵ Twelve studies (N = 741) were included, and 395 patients were treated with MWA versus conventional surgical procedure (n = 346). The mean follow-up duration was 20.5 months. Pooled data analysis showed mean recurrence free rates for MWA at 1, 3, and 5 years were 65.1%, 44.6%, and 34.3%, respectively. Mean OS rates for MWA at 1, 3, and 5 years were 86.7%, 59.6%, and 44.8%, respectively. Mean local recurrence rates for MWA at 3, 6, and 12 months were 96.3%, 89.6%, and 83.7%, respectively.

Section Summary: Hepatic Tumors
For individuals who have an unresectable primary or metastatic hepatic tumor who receive MWA, the evidence includes RCTs, comparative observational studies, and systematic reviews comparing MWA to RFA or TACE and to surgical resection. The body of evidence indicates that MWA is an effective option in patients for whom resection is not an option. Although studies had methodological limitations, they consistently showed that MWA and RFA had similar survival outcomes with up to 5 years of follow-up in patients with a single tumor < 5 cm or up to 3 nodules < 3 cm each. In a meta-analysis of observational studies, patients receiving MWA had higher local recurrence rates and lower survival than those who received resection but the patient populations were not limited to those who had unresectable tumors. Microwave ablation was associated with lower complications, intraoperative blood loss, and hospital length of stay. A single RCT showed that patients with solitary lesions > 3 and < 5 cm treated with combination MWA plus TACE achieved higher overall and progression-free survival compared to MWA or TACE only. However, it is unclear whether patients in this study were classified with unresectable disease.

Unresectable Primary or Metastatic Lung Tumors
Review of Evidence
Systematic Reviews
Three systematic reviews have compared MWA to RFA for lung cancer (Tables 11 to 13).^66,67,68

Nelson et al. (2019) included 12 retrospective observational studies of MWA in patients with primary or metastatic lung tumors.68 The reviewers did not pool results due to clinical and methodological heterogeneity across the studies. The studies varied with regard to patient characteristics (tumor size, histology, number of treated nodules), outcome measures, and technical experience of surgeons performing the procedures. The primary outcome was local recurrence, and survival outcomes were not assessed. Overall, local recurrence rates ranged from 9% to 37% across the studies. Newer reports and those that targeted smaller tumors showed more favorable efficacy rates. Results in patients with multiple tumors were not reported separately. Four studies reported results by tumor size; the local recurrence rates for large tumors ( > 3 or 4 cm depending on the study) were 50%, 75%, 36%, and 26%. In the same 4 studies, for small tumors ( < 3 or 3.5 cm depending on the study), local recurrence rates were 19%, 18%, 18%, and 5%, respectively. The most frequent adverse event with MWA was a pneumothorax requiring a chest tube. The reviewers concluded that MWA may be a useful tool in selected patients who are not ideal surgical candidates.

In a meta-analysis of observational studies, Yuan et al. (2019) found higher OS for patients who received RFA compared to those who received MWA.⁶⁶ However, these estimates were not directly comparable because they came from different sets of studies, and the reviewers concluded that percutaneous RFA and MWA were both effective with a high safety profile. The studies used different patient eligibility criteria (e.g., tumor size, lesion number, age, follow-up). Subgroup analyses by tumor size or tumor number were not possible from the data reported.

Jiang et al. (2018) conducted a network meta-analysis to determine the effectiveness of different ablation techniques in patients with lung tumors.⁶⁷ Tumor size, stage of the disease, and primary versus metastatic disease were not accounted for in the analysis. For MWA, weighted average OS rates were 82.5%, 54.6%, 35.7%, 29.6%, and 16.6% at 1, 2, 3, 4, and 5 years, respectively.

Table 11. Comparison of Trials/Studies Included in SR and MA of MWA in Lung Cancer

MA: meta-analysis; MWA: microwave ablation; SR: systematic review.
^a Studies of MWA only.

Table 12. Characteristics of Systematic Reviews of MWA in Lung Cancer

MWA: microwave ablation; N: sample size; NR: not reported; RCT: randomized controlled trial.

Table 13. Results of Systematic Reviews of MWA in Lung Cancer

CI: confidence interval; MWA: microwave ablation; N: sample size; NA: not applicable; NR: not reported.

Randomized Controlled Trials
There is a single RCT of MWA compared to RFA for lung tumors, conducted by Macchi et al. (2017), (Tables 14 and 15).⁸⁴ Patients were eligible for the study if they had a single tumor up to 5 cm, and up to 5 metastases up to 5 cm. However, at baseline, the mean tumor size was 2.21 cm (standard deviation [SD], 0.89) in the MWA group and 1.64 cm ( SD, 0.80) in the RFA group. Mortality rates at 6 and 12 months did not differ between groups, and complications were significantly lower in the MWA group. Limitations of this study are summarized in Tables 16 and 17 and include its small sample size, lack of reporting on blinding, and relatively short follow-up period (12 months). Results were not reported by tumor size or the number of metastases.

Table 14. Summary of Key RCT Characteristics: MWA versus RFA in Patients with Lung Tumors

MWA: microwave ablation; NR: not reported; RCT: randomized controlled trial; RFA: radiofrequency ablation.

Table 15. Summary of Key RCT Results: MWA versus RFA in Patients With Lung Tumors

MWA: microwave ablation; NR: not reported; RCT: randomized controlled trial; RFA: radiofrequency ablation.

Table 16. Study Relevance Limitations

The study limitations stated in this table are those notable in the current review; this is not a comprehensive gaps assessment.
^a Population key: 1. Intended use population unclear; 2. Clinical context is unclear; 3. Study population is unclear; 4. Study population not representative of intended use.
^b Intervention key: 1. Not clearly defined; 2. Version used unclear; 3. Delivery not similar intensity as comparator; 4. Not the intervention of interest.
^c Comparator key: 1. Not clearly defined; 2. Not standard or optimal; 3. Delivery not similar intensity as intervention; 4. Not delivered effectively.
^d Outcomes key: 1. Key health outcomes not addressed; 2. Physiologic measures, not validated surrogates; 3. No CONSORT reporting of harms; 4. Not establish and validated measurements; 5. Clinical significant difference not prespecified; 6. Clinical significant difference not supported.
^e Follow-Up key: 1. Not sufficient duration for benefit; 2. Not sufficient duration for harms.

Table 17. Study Design and Conduct Limitations

The study limitations stated in this table are those notable in the current review; this is not a comprehensive gaps assessment.
a Allocation key: 1. Participants not randomly allocated; 2. Allocation not concealed; 3. Allocation concealment unclear; 4. Inadequate control for selection bias.
b Blinding key: 1. Not blinded to treatment assignment; 2. Not blinded outcome assessment; 3. Outcome assessed by treating physician.
c Selective Reporting key: 1. Not registered; 2. Evidence of selective reporting; 3. Evidence of selective publication.
d Data Completeness key: 1. High loss to follow-up or missing data; 2. Inadequate handling of missing data; 3. High number of crossovers; 4. Inadequate handling of crossovers; 5. Inappropriate exclusions; 6. Not intent to treat analysis (per protocol for noninferiority trials).
e Power key: 1. Power calculations not reported; 2. Power not calculated for primary outcome; 3. Power not based on clinically important difference.
f Statistical key: 1. Analysis is not appropriate for outcome type: (a) continuous; (b) binary; (c) time to event; 2. Analysis is not appropriate for multiple observations per patient; 3. Confidence intervals and/or p values not reported; 4. Comparative treatment effects not calculated.

Section Summary: Lung Tumors
For individuals who have an unresectable primary or metastatic lung tumor who receive MWA, the evidence includes a single RCT, retrospective observational studies, and systematic reviews of these studies. The body of evidence indicates that MWA is an effective option in patients for whom resection is not an option. In the RCT, direct comparison of MWA and RFA in patients with primary or metastatic lung cancer (mean tumor size, 1.90 cm [ ± 0.89] at baseline) found similar mortality rates up to 12 months of follow-up. In the first of 3 systematic reviews that included 12 retrospective observational studies, local recurrence rates were similar for MWA and RFA at a range of 9 to 47 months of follow-up. In the second systematic review with a meta-analysis, there was lower OS with MWA compared to RFA, but studies were not directly comparable due to clinical and methodological heterogeneity. However, the authors concluded that percutaneous RFA and MWA were both effective with a high safety profile. In the third systematic review using a network meta-analysis, the weighted average OS rates for MWA were 82.5%, 54.6%, 35.7%, 29.6%, and 16.6% at 1, 2, 3, 4, and 5 years, respectively. Limitations of the body of evidence included a lack of controlled studies and heterogeneity across studies. The RCT did not report results by tumor size or the number of metastases. The observational studies included in the systematic reviews did not report sufficient information to assess the effectiveness or safety of MWA in subgroups based on the presence of multiple tumors or total tumor burden. Therefore, conclusions about the evidence sufficiency can only be made about patients with single tumors.

Unresectable Primary or Metastatic Renal Tumors
Review of Evidence
Systematic Reviews
Uhlig et al. (2019) published a systematic review with meta-analyses to compare partial nephrectomy, RFA, cryoablation, and MWA and the effect on oncologic, perioperative, and functional outcomes in studies published from 2005 to 2017.⁹³ Microwave ablation was a treatment in 344 of 24,077 patients and represented in 6 of 47 studies. The review included the single RCT (Guan 2012⁹⁴), which is the only study with results for all 3 outcomes of interest. No new data were included but the review utilized a network meta-analyses technique. Microwave ablation when compared to partial nephrectomy, the comparator of interest, was reported to have a lower procedural complication rate but higher local recurrence and cancer-specific mortality rates.⁹³

In a systematic review and meta-analysis, Katsanos et al. (2014) compared thermal ablation (MWA and RFA) with surgical nephrectomy for small renal tumors (mean size, 2.5 cm).⁹⁵ The analysis included 1 randomized study on MWA⁹⁴ (described below) and 5 cohort studies on RFA (N = 587 patients). In the ablation group, complication rates and renal function declines were significantly higher than in the nephrectomy group (p = .04 and p = .03, respectively). The local recurrence rate was 3.6% in both groups (RR, 0.92; 95% CI, 0.4 to 2.14; p = .79) and disease-free survival up to 5 years did not differ significantly between groups (hazard ratio [HR], 1.04; 95% CI, 0.48 to 2.24; p = .92).

Martin et al. (2013) conducted a meta-analysis comparing MWA with cryoablation for small renal tumors.⁹⁶ The analysis included 7 MWA studies (n = 164 patients) and 44 cryoablation studies (n = 2,989 patients). Selected studies were prospective or retrospective, nonrandomized, and noncomparative. Mean follow-up duration was shorter for MWA (17.86 months) than for cryoablation (30.22 months; p = .07). Mean tumor size was significantly larger in the MWA studies than in the cryoablation studies (2.58 cm vs. 3.13 cm, respectively, p = .04). Local tumor progression (4.07% vs. 2.53%, respectively; p = .46) and progression to metastatic disease (0.8% vs. 0%, respectively; p = .12) did not differ significantly.

Randomized Controlled Trial
Guan et al. (2012) reported on a prospective randomized study that compared the use of MWA with partial nephrectomy (the criterion standard of nephron-sparing surgical resection) for solitary renal tumors less than 4 cm.⁹⁴ Forty-eight patients received MWA and 54 had partial nephrectomy. Patients in the MWA group (6 [23.5%]) had significantly fewer postoperative complications than in the partial nephrectomy group (18 [33.3%]; p = .019). Microwave ablation patients also had significantly less postoperative renal function declines (p < .009) and estimated perioperative blood loss (p < .001) than partial nephrectomy patients. At last follow-up, estimated glomerular filtration rate declines in both groups were similar (p = 1.00). Disease-specific deaths did not occur, and overall local recurrence-free survival by Kaplan-Meier estimates at 3 years was 91.3% for MWA and 96.0% for partial nephrectomy (p = .541).

Case Series and Retrospective Reviews
De Cobelli et al. (2020) reported the results of a retrospective comparative analysis of 83 nodules in 72 consecutive non-surgical candidates treated with cryoablation (n = 44) or MWA (n = 28).⁹⁷ Local recurrence rates were evaluated at 1, 6, 12, and 18 to 24 months post-procedure. Median follow-up was 22 and 20 months in the cryoablation and MWA groups, respectively. Disease recurrence was observed in 3/47 and 1/30 treated nodules in the cryoablation and MWA groups, respectively (p = .06). Recurrences occurred at 6, 12, and 18 months following cryoablation and at 12 months following MWA. No statistically significant differences were observed in nephrometry score (p = .1), technical success (p = .8) or complications (p = .57).

Guo et al. (2020) reported a retrospective review of 106 patients with 119 T1a renal cell carcinoma tumors treated with MWA.⁹⁸ Complete response was achieved in 95.3% of patients (mean tumor diameter, 2.4 cm; range, 1 to 4 cm). Local tumor progression was observed in 6 patients at a mean of 20 months post-procedure. Local progression-free survival rates were 100%, 92.8%, and 90.6% at 1, 2, and 3 years, respectively. Overall survival rates were 99%, 97.7%, and 94.6% at 1, 2, and 3 years, respectively. Complications were reported in 6 patients (5.7%) within 30 days of the procedure, but none of these required intervention.

Aarts et al. (2020) conducted another retrospective review of 100 patients with 108 T1 renal cell carcinomas treated with MWA.⁹⁹ The median tumor size in this study was 3.2 cm (interquartile range, 2.4 to 4 cm). Primary efficacy was achieved for 81% (88/108) of lesions overall, but primary efficacy rates were lower among patients with T1b tumors (52%) versus T1a tumors (89%; p < .001). Secondary efficacy was achieved for 97% (101/103). Over a median follow-up time of 19 months, local tumor recurrence was observed for 4 (4%) tumors.

Muto et al. (2011) reported on complete tumor coagulation necrosis in 10 patients treated with MWA for clear cell renal carcinoma (median tumor size, 2.75 cm).¹⁰⁰ No complications were reported during or after the procedure. Bai et al. (2010) reported complete laparoscopic MWA in 17 of 18 clear cell renal carcinoma tumors (mean tumor size, 2.8 cm).¹⁰¹ In this study, evidence of disease progression was not found at a median follow-up of 20 months. Complications reported were mild (18.2%), and renal function did not significantly deteriorate.

In a study of 10 patients with solid-enhancing renal tumors (median size, 3.65 cm) who were treated with MWA, Castle et al. (2011) reported tumor recurrence in 3 of 8 tumors at a mean follow-up of 17.9 months.¹⁰² Twenty percent of patients experienced intraoperative complications while 40% experienced postoperative complications, including perinephric hematoma, splenic capsular tear, pleuritic chest pain, skin burn, fever, hematuria, genitofemoral neuralgia, and urinoma.

In another study, Guan et al. (2010) reported on the safety of MWA for renal hamartoma.¹⁰³ In this case series, 15 of 16 patients had complete tumor ablation. Disease recurrence was not reported at a median follow-up of 16 months.

Section Summary: Renal Tumors
For individuals who have an unresectable primary or metastatic renal tumor who receive MWA, the evidence includes a single RCT that compared MWA to partial nephrectomy, retrospective reviews, and case series. In the RCT, overall local recurrence-free survival at 3 years was 91.3% for MWA and 96.0% for partial nephrectomy (p = .54). However, there is a lack of controlled studies comparing MWA to other ablation techniques in patients with renal tumors.

Unresectable Primary or Metastatic Solid Tumors Other than Hepatic, Lung, or Renal
Unresectable Primary or Metastatic Breast Tumors
Review of Evidence
Systematic Reviews
A systematic review by Zhao and Wu (2010) assessing ablation techniques for breast cancer found that only 0% to 8% of breast cancer tumors were completely ablated with MWA.¹⁰⁴ The studies identified by reviewers were mostly feasibility and pilot studies conducted in research settings.

Case Series
Zhou et al. (2012) reported on 41 patients treated with MWA directly followed by mastectomy for single breast tumors with a mean volume of 5.26 cm (range, 0.09 to 14.14 cm).¹⁰⁵ Complete tumor ablation was found by microscopic evaluation in 37 (90%) of the 41 tumors ablated (95% CI, 76.9% to 97.3%). Reversible thermal injuries to the skin and pectoralis major muscle occurred in 3 patients.

Other Unresectable Primary or Metastatic Solid Tumors
Review of Evidence
Systematic Reviews
No RCTs on the use of MWA for other tumors or conditions were identified. A systematic review of ablation therapies, including MWA, for locally advanced pancreatic cancer was published by Keane et al. (2014).¹⁰⁶ Reviewers found limited evidence on the use of MWA for pancreatic cancer. Cui et al. (2019) conducted a non-comparative systematic review and meta-analysis of 5 retrospective studies and 2 prospective studies in patients with benign thyroid nodules or papillary thyroid microcarcinoma and found that MWA improved nodule volume and symptom scores in these patients.¹⁰⁷ Wu et al. (2022) conducted a systematic review and meta-analysis comparing MWA versus conventional surgery for the treatment of papillary thyroid microcarcinoma.¹⁰⁸ There were 13 included studies which were all non-randomized. There was no differences between the 2 groups in recurrence rate or lymph node metastasis; however, the MWA group did have a shorter operation time, less intra-operative blood loss, shorter postoperative hospital stay, and few complications.

Case Series
Case studies and retrospective reviews on the use of MWA for adrenal carcinoma,¹⁰⁹ metastatic bone tumors,¹¹⁰ intrahepatic primary cholangiocarcinoma,¹¹¹ pancreatic neuroendocrine tumors,¹¹² and other nononcologic conditions (i.e., bleeding peptic ulcers, esophageal varices, secondary hypersplenism) were identified.

Subsection Summary: Other Solid Tumors
For individuals who have unresectable primary or metastatic solid tumors other than hepatic, lung, or renal. who receive MWA, the evidence includes systematic reviews and case series. No RCTs on the use of MWA for other tumors or conditions were identified.

Summary of Evidence
For individuals who have an unresectable primary or metastatic hepatic tumor who receive MWA, the evidence includes RCTs, comparative observational studies, and systematic reviews comparing MWA to RFA and to surgical resection. Relevant outcomes are OS, disease-specific survival, symptoms, QOL, and treatment-related mortality and morbidity. The body of evidence indicates that MWA is an effective option in patients for whom resection is not an option. Although studies had methodological limitations, results consistently showed that that MWA and RFA had similar survival outcomes with up to 5 years of follow-up in patients with a single tumor < 5 cm or up to 3 nodules < 3 cm each. In a meta-analysis of observational studies, patients receiving MWA had higher local recurrence rates and lower survival than those who received resection, but the patient populations were not limited to those who had unresectable tumors. Microwave ablation was associated with lower complications, intraoperative blood loss, and hospital length of stay. The evidence is sufficient to determine that the technology results in an improvement in the net health outcome.

For individuals who have an unresectable primary or metastatic lung tumor who receive MWA, the evidence includes a single RCT, retrospective observational studies, and systematic reviews of these studies. Relevant outcomes are OS, disease-specific survival, symptoms, QOL, and treatment-related mortality and morbidity. The body of evidence indicates that MWA is an effective option in patients for whom resection is not an option. In the RCT, direct comparison of MWA and RFA in patients with primary or metastatic lung cancer (mean tumor size, 1.90 cm [± 0.89] at baseline) found similar mortality rates up to 12 months of follow-up. In the first of 3 systematic reviews that included 12 retrospective observational studies, local recurrence rates were similar for MWA and RFA at a range of 9 to 47 months of follow-up. In the second systematic review with a meta-analysis, there was lower OS with MWA compared to RFA but studies were not directly comparable due to clinical and methodological heterogeneity. However, the authors concluded that percutaneous RFA and MWA were both effective with a high safety profile. In the third systematic review using a network meta-analysis, the weighted average OS rates for MWA were 82.5%, 54.6%, 35.7%, 29.6%, and 16.6% at 1, 2, 3, 4 and 5 years, respectively. Limitations of the body of evidence included a lack of controlled studies and heterogeneity across studies. The RCT did not report results by tumor size or the number of metastases. The observational studies included in the systematic reviews did not report sufficient information to assess the effectiveness or safety of MWA in subgroups based on the presence of multiple tumors or total tumor burden. Therefore, conclusions about the evidence sufficiency can only be made about patients with single tumors. For this population, the evidence is sufficient to determine that the technology results in an improvement in the net health outcome.

For individuals who have an unresectable primary or metastatic renal tumor who receive MWA, the evidence includes a single RCT that compared MWA to partial nephrectomy, retrospective reviews, systematic reviews, and meta-analyses of the retrospective reviews (with or without the single RCT) and case series. Relevant outcomes are OS, disease-specific survival, symptoms, QOL, and treatment-related mortality and morbidity. In the RCT, overall local recurrence-free survival at 3 years was 91.3% for MWA and 96.0% for partial nephrectomy (p = .54). This positive outcome should be replicated in additional RCTs. There are also no controlled studies comparing MWA to other ablation techniques in patients with renal tumors. The evidence is insufficient to determine that the technology results in an improvement in the net health outcome.

For individuals who have unresectable primary or metastatic solid tumors other than hepatic, lung, or renal who receive MWA, the evidence includes systematic reviews and case series. Relevant outcomes are OS, disease-specific survival, symptoms, QOL, and treatment-related mortality and morbidity. The evidence is insufficient to determine that the technology results in an improvement in the net health outcome.

The purpose of the following information is to provide reference material. Inclusion does not imply endorsement or alignment with the evidence review conclusions.

Clinical Input From Physician Specialty Societies and Academic Medical Centers
While the various physician specialty societies and academic medical centers may collaborate with and make recommendations during this process, through the provision of appropriate reviewers, input received does not represent an endorsement or position statement by the physician specialty societies or academic medical centers, unless otherwise noted.

2016 Input
In response to requests, input was received from 2 physician specialty societies and 1 academic medical center while this policy was under review in 2016. This number of responses was less than optimal. Input overall was mixed. There was some support for the medical necessity of microwave ablation (MWA) in each category, with some reviewers indicating that it was standard of care for certain tumors. However, there were no indications for which all 3 reviewers agreed that MWA should be medically necessary.

2011 Input
In response to requests, input was received from 2 physician specialty societies (3 reviews) and 4 academic medical centers (6 reviews) while this policy was in development. Eight reviewers considered MWA investigational to treat primary tumors such as hepatocellular carcinoma, benign and malignant renal tumors, lung tumors, adrenal tumors, or cholangiocarcinoma. The reviewers noted insufficient evidence and a need for further studies on MWA. However, 1 reviewer indicated MWA for primary tumors, including, but not limited to hepatocellular carcinoma, benign and malignant renal tumors, lung tumors, adrenal tumors, and cholangiocarcinoma, may be considered a treatment option, and another reviewer indicated that MWA for renal tumors may be considered a treatment option.

Four reviewers considered MWA investigational to treat liver metastases, and 2 reviewers indicated MWA for liver metastases may be considered a treatment option. One reviewer noted MWA may be appropriate for tumors not amenable to radiofrequency ablation or other local treatments. This reviewer also suggested MWA may be more appropriate for tumors located near large blood vessels.

Practice Guidelines and Position Statements
Guidelines or position statements will be considered for inclusion in Supplemental Information if they were issued by, or jointly by, a U.S. professional society, an international society with U.S. representation, or National Institute for Health and Care Excellence (NICE). Priority will be given to guidelines that are informed by a systematic review, include strength of evidence ratings, and include a description of management of conflict of interest.

National Comprehensive Cancer Network
The National Comprehensive Cancer Network (NCCN) guidelines on hepatobiliary cancers (v.2.2022 ) list MWA (along with radiofrequency ablation, cryoablation, and percutaneous alcohol injection) as a treatment option for hepatocellular carcinoma (HCC) tumors in patients who are not candidates for potential curative treatments (e.g., resection and transplantation) and do not have large-volume extrahepatic disease.¹¹³ Ablation should only be considered when tumors are accessible by percutaneous, laparoscopic, or open approaches. The guidelines indicate "Ablation alone may be curative in treating tumors less than or equal to 3 cm [...] Lesions 3 to 5 cm may be treated to prolong survival using arterially directed therapies, or with combination of an arterially directed therapy and ablation as long as tumor location is accessible for ablation."

The guidelines on non-small cell lung cancer (NSCLC) (v.3.2022 ) state that image-guided thermal ablation therapies such as cryotherapy, microwave, or radiofrequency may be an option for select medically inoperable patients not receiving stereotactic ablative radiotherapy or definitive radiotherapy.¹¹⁴ Image-guided thermal ablation therapy is considered an option for the management of NSCLC lesions < 3 cm. Ablation for NSCLC lesions > 3 cm has been associated with higher rates of local recurrence and complications.

Guidelines on small-cell lung cancer (v. 1.2023 ) state, "Stereotactic ablative radiotherapy is an option for certain patients with medically inoperable stage I to IIA small-cell lung cancer."¹¹⁵

The network guidelines on neuroendocrine tumors (v.1.2022 ) state that cytoreductive surgery or ablative therapies (e.g., radiofrequency, cryotherapy, microwave) may be considered in patients with progressive hepatic-predominant metastatic disease to reduce tumor bulk and relieve symptoms of hormone hypersecretion (category 2B). Additionally, although prospective data for ablative therapy interventions are limited, the guideline notes that "percutaneous thermal ablation, often using microwave energy, can be considered for oligometastatic liver disease, generally up to 4 lesions each smaller than 3 cm."¹¹⁶

The guidelines on kidney cancer (v.2.2023 ) do not specifically address the role of MWA, but state that other thermal ablation techniques (RFA and cryotherapy) may be an option for T1 renal lesions, particularly for masses < 3 cm.¹¹⁷

The guidelines on breast cancer (v 4.2022. ) do not address thermal ablation techniques such as MWA.¹¹⁸

National Institute for Health and Care Excellence
The National Institute for Health and Care Excellence (2016) updated its guidance on MWA for treatment of metastases in the liver.¹¹⁹ The revised guidance states:

• Current evidence on MWA for treating liver metastases raises no major safety concerns and the evidence on efficacy is adequate in terms of tumor ablation. Therefore this procedure may be used provided that standard arrangements are in place for clinical governance, consent, and audit.
• Patient selection should be carried out by a hepatobiliary cancer multidisciplinary team.
• Further research would be useful for guiding the selection of patients for this procedure. This should document the site and type of the primary tumor being treated, the intention of treatment (palliative or curative), imaging techniques used to assess the efficacy of the procedure, long-term outcomes, and survival.

The Institute (2007) also published guidance on MWA for HCC.¹²⁰ This guidance indicated: “Current evidence on the safety and efficacy of MWA of hepatocellular carcinoma appears adequate to support the use of this procedure.” The guidance also stated there are no major concerns about the efficacy of MWA, but noted that limited, long-term survival data are available.

The Institute (2013) has published guidance on MWA for lung tumors as well.¹²¹ This guidance indicated that "evidence that the procedure improves clinical outcomes and quality of life is limited in quantity and quality. There is a risk of complications, including pneumothorax, which may have serious implications for patients with already compromised lung function. Therefore this procedure should only be used with special arrangements for clinical governance, consent and audit." The guidance encourages further research.

American College of Chest Physicians
The American College of Chest Physicians (2013) evidence-based guidelines on the treatment of NSCLC noted that the role of ablative therapies in the treatment of high-risk patients with stage I NSCLC is evolving.¹²² The guidelines deal mostly with radiofrequency ablation.

American Urological Association
The American Urological Association (2021) updated its guidelines on renal mass and localized renal cancer, which note that both RFA and cryoablation may be offered as options for patients who elect thermal ablation (Conditional Recommendation; Evidence Level: Grade C).¹²³ Thermal ablation can be considered as an alternate approach in the management of T1a solid renal masses < 3 cm. In these patients, a percutaneous technique is preferred (Moderate Recommendation; Evidence Level: Grade C). The guidelines do not specifically address MWA.

U.S. Preventive Services Task Force Recommendations
Not applicable

Ongoing and Unpublished Clinical Trials
Some currently ongoing and unpublished trials that might influence this review are listed in Table 18.

Table 18. Summary of Key Trials

NCT: national clinical trial.
^a Denotes industry-sponsored or cosponsored trial.

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41. Chinnaratha MA, Sathananthan D, Pateria P, et al. High local recurrence of early-stage hepatocellular carcinoma after percutaneous thermal ablation in routine clinical practice. Eur J Gastroenterol Hepatol. Mar 2015; 27(3): 349-54. PMID 25563141
42. Cillo U, Noaro G, Vitale A, et al. Laparoscopic microwave ablation in patients with hepatocellular carcinoma: a prospective cohort study. HPB (Oxford). Nov 2014; 16(11): 979-86. PMID 24750429
43. Correa-Gallego C, Fong Y, Gonen M, et al. A retrospective comparison of microwave ablation vs. radiofrequency ablation for colorectal cancer hepatic metastases. Ann Surg Oncol. Dec 2014; 21(13): 4278-83. PMID 24889486
44. Di Vece F, Tombesi P, Ermili F, et al. Coagulation areas produced by cool-tip radiofrequency ablation and microwave ablation using a device to decrease back-heating effects: a prospective pilot study. Cardiovasc Intervent Radiol. Jun 2014; 37(3): 723-9. PMID 24196263
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46. Kamal A, Elmoety AAA, Rostom YAM, et al. Percutaneous radiofrequency versus microwave ablation for management of hepatocellular carcinoma: a randomized controlled trial. J Gastrointest Oncol. Jun 2019; 10(3): 562-571. PMID 31183208
47. Lee KF, Wong J, Hui JW, et al. Long-term outcomes of microwave versus radiofrequency ablation for hepatocellular carcinoma by surgical approach: A retrospective comparative study. Asian J Surg. Jul 2017; 40(4): 301-308. PMID 26922631
48. Liu Y, Li S, Wan X, et al. Efficacy and safety of thermal ablation in patients with liver metastases. Eur J Gastroenterol Hepatol. Apr 2013; 25(4): 442-6. PMID 23470267
49. Liu W, Zheng Y, He W, et al. Microwave vs radiofrequency ablation for hepatocellular carcinoma within the Milan criteria: a propensity score analysis. Aliment Pharmacol Ther. Sep 2018; 48(6): 671-681. PMID 30063081
50. Sakaguchi H, Seki S, Tsuji K, et al. Endoscopic thermal ablation therapies for hepatocellular carcinoma: a multi-center study. Hepatol Res. Jan 2009; 39(1): 47-52. PMID 18761680
51. Santambrogio R, Chiang J, Barabino M, et al. Comparison of Laparoscopic Microwave to Radiofrequency Ablation of Small Hepatocellular Carcinoma (3 cm). Ann Surg Oncol. Jan 2017; 24(1): 257-263. PMID 27581608
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54. Simo KA, Sereika SE, Newton KN, et al. Laparoscopic-assisted microwave ablation for hepatocellular carcinoma: safety and efficacy in comparison with radiofrequency ablation. J Surg Oncol. Dec 2011; 104(7): 822-9. PMID 21520094
55. Sparchez Z, Mocan T, Hajjar NA, et al. Percutaneous ultrasound guided radiofrequency and microwave ablation in the treatment of hepatic metastases. A monocentric initial experience. Med Ultrason. Aug 31 2019; 21(3): 217-224. PMID 31476199
56. Tian W, Kuang M, Lv M, et al. A randomised comparative trial on liver tumors treated with ultrasound-guided percutaneous radiofrequency versus microwave ablation. Chin J Hepatobiliary Surg 2014;20:11922.
57. van Tilborg AA, Scheffer HJ, de Jong MC, et al. MWA Versus RFA for Perivascular and Peribiliary CRLM: A Retrospective Patient- and Lesion-Based Analysis of Two Historical Cohorts. Cardiovasc Intervent Radiol. Oct 2016; 39(10): 1438-46. PMID 27387188
58. Vietti Violi N, Duran R, Guiu B, et al. Efficacy of microwave ablation versus radiofrequency ablation for the treatment of hepatocellular carcinoma in patients with chronic liver disease: a randomised controlled phase 2 trial. Lancet Gastroenterol Hepatol. May 2018; 3(5): 317-325. PMID 29503247
59. Yang B, Li Y. A comparative study of laparoscopic microwave ablation with laparoscopic radiofrequency ablation for colorectal liver metastasis. J BUON. May-Jun 2017; 22(3): 667-672. PMID 28730772
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61. Zaitoun MMA, Elsayed SB, Zaitoun NA, et al. Combined therapy with conventional trans-arterial chemoembolization (cTACE) and microwave ablation (MWA) for hepatocellular carcinoma 3- 5 cm. Int J Hyperthermia. 2021; 38(1): 248-256. PMID 33615957
62. Loveman E, Jones J, Clegg AJ, et al. The clinical effectiveness and cost-effectiveness of ablative therapies in the management of liver metastases: systematic review and economic evaluation. Health Technol Assess. Jan 2014; 18(7): vii-viii, 1-283. PMID 24484609
63. Bala MM, Riemsma RP, Wolff R, et al. Microwave coagulation for liver metastases. Cochrane Database Syst Rev. Oct 13 2013; (10): CD010163. PMID 24122576
64. Pathak S, Jones R, Tang JM, et al. Ablative therapies for colorectal liver metastases: a systematic review. Colorectal Dis. Sep 2011; 13(9): e252-65. PMID 21689362
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66. Yuan Z, Wang Y, Zhang J, et al. A Meta-Analysis of Clinical Outcomes After Radiofrequency Ablation and Microwave Ablation for Lung Cancer and Pulmonary Metastases. J Am Coll Radiol. Mar 2019; 16(3): 302-314. PMID 30642784
67. Jiang B, Mcclure MA, Chen T, et al. Efficacy and safety of thermal ablation of lung malignancies: A Network meta-analysis. Ann Thorac Med. Oct-Dec 2018; 13(4): 243-250. PMID 30416597
68. Nelson DB, Tam AL, Mitchell KG, et al. Local Recurrence After Microwave Ablation of Lung Malignancies: A Systematic Review. Ann Thorac Surg. Jun 2019; 107(6): 1876-1883. PMID 30508527
69. He W, Hu XD, Wu DF, et al. Ultrasonography-guided percutaneous microwave ablation of peripheral lung cancer. Clin Imaging. Jul-Aug 2006; 30(4): 234-41. PMID 16814137
70. Wolf FJ, Grand DJ, Machan JT, et al. Microwave ablation of lung malignancies: effectiveness, CT findings, and safety in 50 patients. Radiology. Jun 2008; 247(3): 871-9. PMID 18372457
71. Vogl TJ, Naguib NN, Gruber-Rouh T, et al. Microwave ablation therapy: clinical utility in treatment of pulmonary metastases. Radiology. Nov 2011; 261(2): 643-51. PMID 22012906
72. Lu Q, Cao W, Huang L, et al. CT-guided percutaneous microwave ablation of pulmonary malignancies: Results in 69 cases. World J Surg Oncol. May 07 2012; 10: 80. PMID 22564777
73. Carrafiello G, Mangini M, Fontana F, et al. Microwave ablation of lung tumours: single-centre preliminary experience. Radiol Med. Jan 2014; 119(1): 75-82. PMID 24234180
74. Liu H, Steinke K. High-powered percutaneous microwave ablation of stage I medically inoperable non-small cell lung cancer: a preliminary study. J Med Imaging Radiat Oncol. Aug 2013; 57(4): 466-74. PMID 23870347
75. Vogl TJ, Worst TS, Naguib NN, et al. Factors influencing local tumor control in patients with neoplastic pulmonary nodules treated with microwave ablation: a risk-factor analysis. AJR Am J Roentgenol. Mar 2013; 200(3): 665-72. PMID 23436860
76. Wei Z, Ye X, Yang X, et al. Microwave ablation in combination with chemotherapy for the treatment of advanced non-small cell lung cancer. Cardiovasc Intervent Radiol. Feb 2015; 38(1): 135-42. PMID 24809754
77. Yang X, Ye X, Zheng A, et al. Percutaneous microwave ablation of stage I medically inoperable non-small cell lung cancer: clinical evaluation of 47 cases. J Surg Oncol. Nov 2014; 110(6): 758-63. PMID 24965604
78. Zheng A, Wang X, Yang X, et al. Major complications after lung microwave ablation: a single-center experience on 204 sessions. Ann Thorac Surg. Jul 2014; 98(1): 243-8. PMID 24793688
79. Acksteiner C, Steinke K. Percutaneous microwave ablation for early-stage non-small cell lung cancer (NSCLC) in the elderly: a promising outlook. J Med Imaging Radiat Oncol. Feb 2015; 59(1): 82-90. PMID 25335916
80. Wei Z, Ye X, Yang X, et al. Microwave ablation plus chemotherapy improved progression-free survival of advanced non-small cell lung cancer compared to chemotherapy alone. Med Oncol. Feb 2015; 32(2): 464. PMID 25572816
81. Egashira Y, Singh S, Bandula S, et al. Percutaneous High-Energy Microwave Ablation for the Treatment of Pulmonary Tumors: A Retrospective Single-Center Experience. J Vasc Interv Radiol. Apr 2016; 27(4): 474-9. PMID 26944360
82. Ko WC, Lee YF, Chen YC, et al. CT-guided percutaneous microwave ablation of pulmonary malignant tumors. J Thorac Dis. Oct 2016; 8(Suppl 9): S659-S665. PMID 28066666
83. Li B, Wang Z, Zhou K, et al. Safety and feasibility within 24 h of discharge in patents with inoperable malignant lung nodules after percutaneous microwave ablation. J Cancer Res Ther. Dec 2016; 12(Supplement): C171-C175. PMID 28230012
84. Macchi M, Belfiore MP, Floridi C, et al. Radiofrequency versus microwave ablation for treatment of the lung tumours: LUMIRA (lung microwave radiofrequency) randomized trial. Med Oncol. May 2017; 34(5): 96. PMID 28417355
85. Maxwell AW, Healey TT, Dupuy DE. Percutaneous Thermal Ablation for Small-Cell Lung Cancer: Initial Experience with Ten Tumors in Nine Patients. J Vasc Interv Radiol. Dec 2016; 27(12): 1815-1821. PMID 27776982
86. Vogl TJ, Eckert R, Naguib NN, et al. Thermal Ablation of Colorectal Lung Metastases: Retrospective Comparison Among Laser-Induced Thermotherapy, Radiofrequency Ablation, and Microwave Ablation. AJR Am J Roentgenol. Dec 2016; 207(6): 1340-1349. PMID 27680945
87. Zheng A, Ye X, Yang X, et al. Local Efficacy and Survival after Microwave Ablation of Lung Tumors: A Retrospective Study in 183 Patients. J Vasc Interv Radiol. Dec 2016; 27(12): 1806-1814. PMID 27789077
88. Healey TT, March BT, Baird G, et al. Microwave Ablation for Lung Neoplasms: A Retrospective Analysis of Long-Term Results. J Vasc Interv Radiol. Feb 2017; 28(2): 206-211. PMID 27993505
89. Nour-Eldin NA, Exner S, Al-Subhi M, et al. Ablation therapy of non-colorectal cancer lung metastases: retrospective analysis of tumour response post-laser-induced interstitial thermotherapy (LITT), radiofrequency ablation (RFA) and microwave ablation (MWA). Int J Hyperthermia. Nov 2017; 33(7): 820-829. PMID 28540791
90. Wei Z, Ye X, Yang X, et al. Advanced non small cell lung cancer: response to microwave ablation and EGFR Status. Eur Radiol. Apr 2017; 27(4): 1685-1694. PMID 27436020
91. Yang X, Ye X, Huang G, et al. Repeated percutaneous microwave ablation for local recurrence of inoperable Stage I nonsmall cell lung cancer. J Cancer Res Ther. 2017; 13(4): 683-688. PMID 28901314
92. Zhong L, Sun S, Shi J, et al. Clinical analysis on 113 patients with lung cancer treated by percutaneous CT-guided microwave ablation. J Thorac Dis. Mar 2017; 9(3): 590-597. PMID 28449467
93. Uhlig J, Strauss A, Rucker G, et al. Partial nephrectomy versus ablative techniques for small renal masses: a systematic review and network meta-analysis. Eur Radiol. Mar 2019; 29(3): 1293-1307. PMID 30255245
94. Guan W, Bai J, Liu J, et al. Microwave ablation versus partial nephrectomy for small renal tumors: intermediate-term results. J Surg Oncol. Sep 01 2012; 106(3): 316-21. PMID 22488716
95. Katsanos K, Mailli L, Krokidis M, et al. Systematic review and meta-analysis of thermal ablation versus surgical nephrectomy for small renal tumours. Cardiovasc Intervent Radiol. Apr 2014; 37(2): 427-37. PMID 24482030
96. Martin J, Athreya S. Meta-analysis of cryoablation versus microwave ablation for small renal masses: is there a difference in outcome?. Diagn Interv Radiol. Nov-Dec 2013; 19(6): 501-7. PMID 24084196
97. De Cobelli F, Papa M, Panzeri M, et al. Percutaneous Microwave Ablation Versus Cryoablation in the Treatment of T1a Renal Tumors. Cardiovasc Intervent Radiol. Jan 2020; 43(1): 76-83. PMID 31451888
98. Guo J, Arellano RS. Percutaneous Microwave Ablation of Category T1a Renal Cell Carcinoma: Intermediate Results on Safety, Technical Feasibility, and Clinical Outcomes of 119 Tumors. AJR Am J Roentgenol. Jan 2021; 216(1): 117-124. PMID 32603227
99. Aarts BM, Prevoo W, Meier MAJ, et al. Percutaneous Microwave Ablation of Histologically Proven T1 Renal Cell Carcinoma. Cardiovasc Intervent Radiol. Jul 2020; 43(7): 1025-1033. PMID 32052093
100. Muto G, Castelli E, Migliari R, et al. Laparoscopic microwave ablation and enucleation of small renal masses: preliminary experience. Eur Urol. Jul 2011; 60(1): 173-6. PMID 21531501
101. Bai J, Hu Z, Guan W, et al. Initial experience with retroperitoneoscopic microwave ablation of clinical T(1a) renal tumors. J Endourol. Dec 2010; 24(12): 2017-22. PMID 20932080
102. Castle SM, Salas N, Leveillee RJ. Initial experience using microwave ablation therapy for renal tumor treatment: 18-month follow-up. Urology. Apr 2011; 77(4): 792-7. PMID 21324512
103. Guan W, Bai J, Hu Z, et al. Retroperitoneoscopic microwave ablation of renal hamartoma: middle-term results. J Huazhong Univ Sci Technolog Med Sci. Oct 2010; 30(5): 669-71. PMID 21063854
104. Zhao Z, Wu F. Minimally-invasive thermal ablation of early-stage breast cancer: a systemic review. Eur J Surg Oncol. Dec 2010; 36(12): 1149-55. PMID 20889281
105. Zhou W, Zha X, Liu X, et al. US-guided percutaneous microwave coagulation of small breast cancers: a clinical study. Radiology. May 2012; 263(2): 364-73. PMID 22438362
106. Keane MG, Bramis K, Pereira SP, et al. Systematic review of novel ablative methods in locally advanced pancreatic cancer. World J Gastroenterol. Mar 07 2014; 20(9): 2267-78. PMID 24605026
107. Cui T, Jin C, Jiao D, et al. Safety and efficacy of microwave ablation for benign thyroid nodules and papillary thyroid microcarcinomas: A systematic review and meta-analysis. Eur J Radiol. Sep 2019; 118: 58-64. PMID 31439259
108. Wu X, Jiang Z, Liu J, et al. The efficacy and safety of microwave ablation versus conventional open surgery for the treatment of papillary thyroid microcarcinoma: a systematic review and meta-analysis. Gland Surg. Jun 2022; 11(6): 1003-1014. PMID 35800741
109. Li X, Fan W, Zhang L, et al. CT-guided percutaneous microwave ablation of adrenal malignant carcinoma: preliminary results. Cancer. Nov 15 2011; 117(22): 5182-8. PMID 21523760
110. Pusceddu C, Sotgia B, Fele RM, et al. Treatment of bone metastases with microwave thermal ablation. J Vasc Interv Radiol. Feb 2013; 24(2): 229-33. PMID 23200605
111. Yu MA, Liang P, Yu XL, et al. Sonography-guided percutaneous microwave ablation of intrahepatic primary cholangiocarcinoma. Eur J Radiol. Nov 2011; 80(2): 548-52. PMID 21300500
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