Percutaneous microwave ablation of cT1b renal cell carcinoma: Safety and oncologic efficacy in a large, single-center elderly and comorbid cohort

Purpose: To evaluate safety and oncologic efficacy of percutaneous microwave ablation (MWA) for treating clinically localized T1b (cT1b) renal cell carcinoma (RCC). Methods: This single-center retrospective study was performed under a waiver of informed consent. Seventy-four consecutive patients (49M/25F) with 76 cT1b RCC (median tumor diameter 4.5 cm) were treated with percutaneous MWA between 5/2012 and 8/2020. Patients were stratified into two groups by technique, depending on whether antennas were repositioned for additional ablation or not. Primary efficacy, complications, and local tumor progression (LTP) were compared using the Wilcoxon rank sum and Fisher’s exact tests. The Kaplan Meier method was used for survival analysis. Results: Patients were elderly (median age 69.5), obese (median BMI 34.5) and comorbid (Charlson Comorbidity Index = 4). Most tumors were low-grade (grade 1-2) (67/89, 88%) and clear cell RCC was the most common histology (62/76, 82%). A median of three MWA antennas were powered at 65W for 7 min for treatment. Renal masses were larger (4.6 vs 4.5 cm, p=0.01) and procedure times longer (100 min vs 80.5 min, p=0.04) for the antenna reposition cohort (n=34, 45%). Primary efficacy and high-grade complication rates were 93% and 8%, respectively. The local tumor progression rate (LTP), at a median follow-up was 28.2 months, was 16%. Primary efficacy, low and high-grade complications, change in estimated glomerular filtration rate and LTP were similar between cohorts (p=0.20-0.55). Conclusion: Percutaneous MWA for cT1b RCC is safe in elderly and comorbid patients with acceptable oncologic efficacy. Repeat ablation is well-tolerated and can improve oncologic efficacy.