Is microwave ablation more effective than radiofrequency ablation in achieving local control for primary pulmonary malignancy? Free

Abstract

A best evidence topic in thoracic surgery was written according to a structured protocol. The question addressed was ‘Is microwave ablation (MWA) more effective than radiofrequency ablation (RFA) in achieving local control for primary lung cancer?’. Altogether, 439 papers were found, of which 7 represented the best evidence to answer the clinical question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated. Both are thermal ablative techniques, with microwave ablation (MWA) the newer technique and radiofrequency ablation (RFA) with a longer track record. Lack of consensus with regard to definitions of technical success and efficacy and heterogeneity of study inclusions limits studies for both. The only direct comparison study does not demonstrate a difference with either technique in achieving local control. The quality of evidence for MWA is very limited by retrospective nature and heterogeneity in technique, power settings and tumour type. Tumour size and late-stage cancer were shown to be associated with higher rates of local recurrence in 1 MWA study. RFA studies were generally of a higher level of evidence comprising prospective trials, systematic review and meta-analysis. The recurrence rates for MWA and RFA overlapped, and for the included studies ranged between 16% and 44% for MWA and 9% and 58% for RFA. The current evidence, therefore, does not clearly demonstrate a benefit of MWA over RFA in achieving local control in primary lung cancer.

INTRODUCTION

A best evidence topic was constructed according to a structured protocol. This is fully described in the ICVTS [1].

THREE-PART QUESTION

In [patients receiving thermal ablation for primary lung cancer], is [microwave ablation or radiofrequency ablation] more effective at [achieving local control]?

CLINICAL SCENARIO

You are discussing therapeutic options with a patient who has stage 1A non-small-cell lung cancer (NSCLC) who is unfit for surgery. Normally, you would offer radiofrequency ablation (RFA), but a colleague recently informed you that a newer technique, microwave ablation (MWA), can be used to create a larger ablation zone and has a reduced rate of local recurrence. You resolve to check the literature to compare the 2 techniques for use in primary lung cancer.

SEARCH STRATEGY

An English-language literature review was performed on MEDLINE for the period from January 2000 to March 2018 using the PubMed interface: (thermal ablation OR radiofrequency ablation OR microwave ablation) AND (lung cancer OR primary lung cancer OR non-small cell lung cancer OR primary pulmonary malignancy OR primary pulmonary cancer OR primary lung tumours OR NSLC OR lung tumours) AND (local control OR local recurrence OR local efficacy OR trial OR clinical analysis).

SEARCH OUTCOME

Four hundred and thirty-nine papers were found using the reported search. From these, 7 papers were identified that provided the best evidence to answer the question and are presented in Table 1.

RESULTS

There was only one direct comparison between MWA and RFA which included patients with primary lung cancer.

Macchi et al. [2] randomized 52 patients with stage IV NSCLC to 2 intervention arms, RFA and MWA. The RFA group had a greater percentage of patients demonstrating contrast enhancement at 12 months which is presumed to represent tumour recurrence: RFA 25% vs MWA 6.25%, suggesting favourable rates of local control in the MWA group. However, despite clinical end points stated to be technical success and clinical effectiveness, these criteria are not addressed in the results with statistical comparison. A further limitation of this study is that its definition of stage IV disease, whether IVa or IVb and according to which edition of tumour, node and metastasis (TNM) lung cancer staging has not been clearly defined.

Very limited studies have examined MWA effectiveness solely in primary lung malignancy, with the majority of studies combining primary lung cancers with pulmonary metastases from remote primary sites. Importantly, the technique has evolved over time with a trend to higher microwave power, which has been shown in pulmonary metastases to achieve superior local control. Three retrospective MWA studies represented the best-quality evidence to answer the clinical question in primary lung cancer.

Zhong et al. [3] showed local progression in 15.9% in a cohort of 113 patients with primary lung malignancy treated with high power MWA (100 W). Further analysis was carried out by separating the cohort into early-stage and late-stage cancer groups and by tumour size. This analysis demonstrated that late-stage cancer or tumour size >3 cm was significantly associated with lower rates of local control, but overall, the study was limited by the use of RECIST criteria which are inappropriate to evaluate postablation response, as it is only validated in the assessment of solid tumour response to chemotherapy.

There are no further studies addressing primary lung cancer alone. However, Zheng et al. [4] performed a study with a high proportion of primary lung cancer (75%) which showed a local progression rate of 19.1% in a cohort of 183 patients following MWA ablation. Overall, this study had a long duration of follow-up of 34.5 months, which showed emphysema and tumour diameter to be significantly associated with local progression. Healey et al. [5] performed a retrospective cohort study of MWA in patients with single lung tumours with a high proportion of primary lung cancer of around 80%. The study had clear outcome definitions and end points, and the Kaplan–Meier analysis reported 78% local control at 1 year, 64% at 2 years and 56% at 3 years. However, a criticism of the study is that microwave technique and power settings varied depending on user preference, and the study involved patients with heterogeneous tumour type and previous treatment. Patients treated earlier and therefore with longer follow-up time periods were treated with low-power MWA, and this may bias the results to higher recurrence rates at longer duration of follow-up.

Three RFA studies represented the best-quality evidence to answer our clinical question. They comprise a higher level of evidence than seen for MWA, with some studies addressing primary lung malignancy alone.

Dupuy et al. [6] conducted a well-designed prospective multicentre RFA trial for stage IA NSCLC (ALLIANCE trial) which had strict enrolment criteria and represents the most robust original evidence for RFA in primary lung cancer. All patients had biopsy-proven cancer deemed medically inoperable. Patients had strict follow-up time points for repeat pulmonary function tests and contrast-enhanced computed tomography (CT), with the first 30 patients also receiving fluorodeoxyglucose (FDG) positron emission tomography (PET) scans at specific time-point intervals. Any growth in the target lesion 1.25 times any dimension compared with baseline scan was considered suspicious for recurrence, with a biopsy being performed if clinically suitable. They found that at 24 months, the local recurrence rate was 29.4% (15/51), all of which occurred in the tumour bed.

Despite being an older study, the RAPTURE trial conducted by Lencioni et al. [7] represented seminal evidence for RFA in primary lung cancer, with its prospective multicentre design and therefore relatively low risk bias compared to the other studies in the RFA literature. It was an intention-to-treat single-arm trial that included 183 lung tumours (including both primary lung and metastatic disease), which demonstrated local recurrence in 3 of 24 patients with NSCLC for whom they had at least 12 months of follow-up. Limitations of this study include its use of RECIST criteria to determine treatment response, heterogeneous patient population and an insufficient follow-up period to detect late tumour recurrences.

A systematic review and meta-analysis by Bi et al. [8] compared stereotactic ablation radiation with RFA in patients with inoperable stage I lung cancer. The meta-analysis included 19 studies reporting local control rates, 5 of which had a 5-year follow-up. It pooled the studies according to the length of follow-up received by patients and found the local control rate of RFA to be 77% in the 1-year follow-up pool, 48% in the 2-year pool and 55% in the 3-year pool.

CLINICAL BOTTOM LINE

There is only one relevant study directly comparing RFA with MWA, which does not clearly demonstrate a benefit of one technique over the other. Lack of consensus with regard to definitions of technical success and efficacy, and heterogeneity of study inclusions limit studies for both. For the microwave studies, there is variation in the power used. Overall, the recurrence rates for MWA and RFA overlapped, and for the included studies ranged between 16% and 44% for MWA and 9% and 58% for RFA. The current evidence, therefore, does not clearly demonstrate a benefit of MWA over RFA in achieving local control in primary lung cancer.

Conflict of interest: none declared.

REFERENCES