Active Surveillance versus Primary Intervention for Clinical T1a Kidney Tumors: Twelve-Year Experience of the DISSRM Prospective Comparative Study.

PURPOSE Active surveillance (AS) is an alternative to primary intervention (PI) in the management of small renal masses (SRMs; clinical stage T1a). However, AS remains underutilized due to a lack of strong, prospective data. We herein report mature outcomes after a twelve-year experience with the Delayed Intervention and Surveillance for Small Renal Masses (DISSRM) Registry. MATERIALS AND METHODS Multi-institutional prospective comparative study from 2009 to 2022 of patients with SRM who chose to undergo AS or PI. Primary outcomes were cancer-specific survival (CSS) and overall survival (OS). RESULTS A total of 958 patients were enrolled; 581 chose AS, and 377 chose PI. Ultimately, 88 of 581 AS patients crossed over to delayed intervention (DI). The median follow-up time for the registry was 4.15 years (IQR 2.11-7.31) among patients who were still alive, with 406 patients followed for ≥5 years. Competing-risk CSS cumulative incidence function (CIF) accounting for other causes of mortality for AS at 4 years and beyond is 0.19% (95% CI; 0.3% - 1.4%), and for PI at 4 years and beyond is 0.68% (95% CI; 0.17% - 2.7%). Gray's test for statistical differences between CSS CI curves of PI vs AS showed no statistical difference (P=0.4). However, Kaplan-Meier analysis of OS showed to be higher in patients undergoing PI compared to AS at 4 years (95% vs 88%), 6 years (92% vs 81%), 8 years (90% vs 66%), and 10 years (85% vs 64%), this difference was statistically significant; log-rank P<0.001. CONCLUSIONS In our study cohort, AS is not inferior to PI in patients with SRM suspicious for renal cell carcinoma. Difference in OS between AS and PI is most likely attributable to the increased risk of death from competing causes among AS patients. A priori definitions of progression, including growth rate, should be re-considered.