Incidence of Local Treatment and Metastasis During Active Surveillance for Patients With a Small Renal Mass in a National Multicenter Prospective Cohort

PURPOSE: The objective of this study was to determine the incidence of local treatment and incidence of metastasis for patients with a solitary small renal mass (SRM; ≤4 cm) initiating active surveillance (AS). MATERIALS AND METHODS: Patients enrolled in the Canadian Kidney Cancer information system between January 2011 and January 2023 with a solitary renal mass ≤ 4 cm opting for AS were included. The primary outcome was local treatment progression, achieved if the patient received definitive local treatment after initiating AS. The secondary outcomes were growth rate progression (>0.5 cm/y), size progression (>4 cm), composite progression (either size or growth rate progression), and development of metastases. RESULTS: The Canadian Kidney Cancer information system included 1393 patients who initiated AS for an SRM ≤ 4 cm during the study period. At a median follow-up of 4.0 years (95% CI 2.1-6.4), 238 patients received local treatment, and of these, 195 were nephron sparing. Two- and 5-year cumulative incidence of treatment was 8.4% (95% CI 6.9-10) and 21% (95% CI 19-24), respectively. Twenty-nine patients developed metastasis. Two- and 5-year cumulative incidence of metastasis was 0.67% (95% CI 0.32-1.3) and 2.3% (95% CI 1.5-3.5), respectively. Of the 29 patients who developed metastases, 23 had progressed using size or growth rate cutoffs, and 7 had received local treatment with curative intent before the identification of metastases. CONCLUSIONS: Patients choosing surveillance for an SRM have low cumulative incidence of local treatment and metastasis at 5 years, demonstrating AS is a safe initial management approach.