PD33-09: Multi-institutional report of patient characteristics and oncologic outcomes following microwave ablation of biopsy-proven renal cell carcinoma

Leo Dreyfuss*, New York, NY, Arighno Das, Madison, WI, Kimberly Maciolek, Charlottesville, VA, Rand Wilcox Vanden Berg, New York, NY, Glenn Allen, Madison, WI, Jonathan Fainberg, New York, NY, Tudor Borza, Shane Wells, Madison, WI, Stephen Culp, Charlottesville, VA, E. Jason Abel, Madison, WI, Timothy McClure, New York, NY

Introduction: CT-guided thermal ablation is an option for the treatment of small renal masses.  Patients with comorbidities may not tolerate extirpative surgery for localized renal cell carcinoma (RCC) and microwave ablation (MWA) may be considered.  We report patient characteristics and outcomes following MWA of biopsy-proven RCC at three high-volume centers.

Methods: Consecutive patients with localized, non-metastatic, pathologically confirmed RCC treated with MWA at three centers were included. Images were reviewed by abdominal radiologists experienced with ablation. Contrast-enhanced CT was performed immediately following ablation to confirm technical success. Surveillance included abdominal cross-sectional imaging at 3-6 month intervals for 2 years and yearly thereafter. Local recurrence was defined radiographically as enhancing tumor within the ablation site following complete ablation.

Results: 541 ablations were performed in 492 patients. Patients with hereditary RCC syndromes (n=15), prior RCC (n=107), multifocal/bilateral tumors (n= 82), and benign/negative biopsy (n=27) were excluded. Final analysis included 370 patients (median age 68; 139 female) with sporadic, biopsy-proven RCC. 

307 patients had cT1a tumors and 63 patients had cT1b or greater tumors. Compared with T1a tumors, patients with T1b tumors had higher body mass index, Charlson Comorbidity index, and ECOG performance status (p < 0.05) but did not differ in gender or age. T1b tumors were more likely to be clear cell RCC (p=0.010) and high grade (0.028). 

32 patients developed recurrences at a median time of 12 (IQR 6-26) months. Local recurrence free survival in the entire cohort was 88.7% at 36 months, 92.1% (95% CI 86.6-95.5) for T1a and 88.1% (95% CI 69.8-95.7) for T1b. Local recurrence free survival improved to 97.3% (95% CI 93.6-98.9) when repeat ablations were included in the analysis. Metastatic free survival was 98.2% at 36 months for all patients, 98.8% (95% CI 96.4-99.6) for T1a and 94.8% (95% CI 80.2-98.7) for T1b. RCC subtype and tumor grade were not associated with local recurrence in patients with T1a tumors. For T1b patients, high tumor grade was predictive of local recurrence (p=0.037).

Conclusions: In this multi-institutional series of biopsy-proven RCC, metastatic spread was rare following MWA. Local control can be achieved for cT1a and cT1b tumors, though multiple ablation sessions may be necessary. Microwave ablation for cT1b masses may be a viable option for patients with medical comorbidities precluding surgical management.

Source of Funding: None