Safety and efficacy of RFA versus MWA for T1a renal cell carcinoma: a propensity score analysis

Percutaneous radiofrequency ablation (RFA) is stated as a treatment option for renal cell carcinoma (RCC) smaller than 4 cm (T1a). Microwave ablation (MWA) is a newer technique and is still considered experimental in some guidelines. The objective of this study was to compare the safety and efficacy of RFA and MWA for the treatment of RCC. Patients with T1a RCC treated by RFA or MWA in two referral centers were retrospectively analyzed. Patient records were evaluated to generate mRENAL nephrometry scores. Local tumor progression (LTP) was considered when new (recurrence) or residual tumor enhancement within/adjacent to the ablation zone was objectified. Differences in LTP-free interval (residual + recurrence) between ablation techniques were assessed with Cox proportional hazards models and propensity score (PS) methods. In 164 patients, 87 RFAs and 101 MWAs were performed for 188 RCCs. The primary efficacy rate was 92% (80/87) for RFA and 91% (92/101) for MWA. Sixteen patients had residual disease (RFA (n = 7), MWA (n = 9)) and 9 patients developed recurrence (RFA (n = 7), MWA (n = 2)). LTP-free interval was significantly worse for higher mRENAL nephrometry scores. No difference in LTP-free interval was found between RFA and MWA in a model with inverse probability weighting using PS (HR = 0.99, 95% CI 0.35-2.81, p = 0.98) and in a PS-matched dataset with 110 observations (HR = 0.82, 95% CI 0.16-4.31, p = 0.82). Twenty-eight (14.9%) complications (Clavien-Dindo grade I-IVa) occurred (RFA n = 14, MWA n = 14). Primary efficacy for ablation of RCC is high for both RFA and MWA. No differences in efficacy and safety were observed between RFA and MWA. Both RFA and MWA are safe and effective ablation techniques in the treatment of T1a renal cell carcinomas. High modified RENAL nephrometry scores are associated with shorter local tumor progression-free interval. MWA can be used as heat-based ablation technique comparable to RFA for the treatment of T1a renal cell carcinomas.