Abstract
BACKGROUND AND OBJECTIVE: In Michigan, around 50% of patients with localized renal masses of ≤7 cm (cT1RMs) are managed without immediate intervention, contradicting previous reports indicating active surveillance (AS) rates of <10-20%. Questions remain regarding the durability of AS when applied so broadly. We evaluated the oncologic outcomes of patients at 1, 2, and 3 yr after the initiation of AS, including survival and delayed intervention rates, hypothesizing that these will be comparable to prior reports. METHODS: Between May 2017 and September 2023, data regarding 2161 (52% of 4178) patients with cT1RMs who initiated AS at Michigan Urological Surgery Improvement Collaborative (MUSIC) practices were reviewed. Factors associated with staying on AS were analyzed. Overall survival and the cumulative incidence of treatment were assessed using the Kaplan-Meier method. KEY FINDINGS AND LIMITATIONS: In total, 2161 patients from 21 practices initiated AS, including 51% with tumors of ≤2 cm, 26% with tumors of 2.1-3.0 cm, and 24% with tumors of 3.1-7.0 cm. At 36 mo, overall survival was 90%, with metastasis and death from kidney cancer in only one patient who refused intervention. The cumulative incidence rates of treatment were 6%, 11%, and 13% at 1, 2, and 3 yr, respectively, with 9.6% for ≤2 cm, 16% for 2.1-3.0 cm, and 18% for >3 cm tumors at 3 yr. Limitations include the study's retrospective review of prospectively enrolled data limiting conclusions beyond 3 yr of follow-up. CONCLUSIONS AND CLINICAL IMPLICATIONS: MUSIC practices initiate AS for >50% of patients with 13% incidence of delayed intervention and <1% incidence of metastasis within 3 yr, indicating that AS is a safe and durable option for many patients with cT1RMs. Further investigations into imaging protocols and longer-term outcomes of AS are warranted. PATIENT SUMMARY: In Michigan, most patients diagnosed with localized renal masses of <4 cm and some with tumors up to 7 cm in size elect active surveillance (AS), with a 13% cumulative incidence of undergoing intervention within 3 yr of detection. At 3 yr after initiating AS, the cohort had 90% overall survival and >99% cancer-specific survival, indicating that AS is a safe and durable strategy.