Abstract No. 229 Eight-Year Follow-Up After Microwave Ablation of Biopsy-Proven cT1a Renal Cell Carcinomas at a Single Institution

Management of small renal masses (SRMs) with ablation is increasing. Microwave ablation (MWA) is newer ablation technology that may have advantages compared to other thermal techniques, including decreased ablation time and heat sink effect. Oncologic outcomes for biopsy-proven renal cell carcinoma (RCC) patients treated with CT-guided MWA are reported. SRMs undergoing CT-guided percutaneous microwave ablation from 2015-2022 were retrospectively reviewed for clinical, pathologic, radiologic, and oncologic data after institutional review board approval. Post-ablation surveillance imaging occurred immediately in the procedure suite, at three months, and annually. Primary outcomes were recurrence (primary and secondary efficacy) and all-cause mortality. Local recurrence was defined as radiologic evidence of enhancement on imaging within or immediately adjacent to the ablation bed. Disease progression was defined as recurrence in either kidney distant from the ablation site or metastatic disease in a new organ. A Kaplan-Meier survival analysis was conducted, including progression-free rates and all-cause mortality. 257 patients underwent MWA treatment during the study period. Patients with benign or non-RCC pathologies, greater than stage 1 RCC, and known RCC syndromes were excluded; 212 patients were included in the analysis. Patient and tumor characteristics are shown in Table 229.1. Median (IQR) duration of follow-up time was 27.0 months (15.0, 45.0), during which time recurrences occurred in 24 patients (11.3%) at a median of 21.0 months (13.5, 29.5). Local recurrence rate was 4.7% with a primary and secondary treatment efficacy was 93.3% and 99.5%. One patient had a local recurrence treated with nephrectomy that then progressed to metastatic disease. At 30 months, the progression-free rate was 98.9% and all-cause mortality rate was 5.8%. This retrospective study supports the use of MWA for patients with SRMs and appropriate surveillance.