Outcomes After Initial Noninterventional Management of Clinical Stage cT1b Renal Masses.

Background and objective: Localized renal masses 4.1-7.0 cm in size (cT1bRMs) are typically treated with partial or radical nephrectomy. Utilization and results of initial nonsurgical approaches for cT1bRMs are unclear. Our primary objective was to evaluate overall (OS) and metastasis-free (MFS) survival after initiating surveillance for cT1bRMs. Methods: We retrospectively examined initial management and subsequent follow-up of all patients diagnosed with cT1bRMs (from May 2017 to November 2024) in the Michigan Urological Surgery Improvement Collaborative (MUSIC). Patients were stratified by intervention versus surveillance at 90 d following initial consultation. Patients initiating surveillance were further stratified as those with continued surveillance versus delayed intervention (DI) at least 90 d after initiating surveillance. The 3-yr estimated rates of DI, OS, MFS, and cancer-specific survival (CSS) were reported. Key findings and limitations: Of 1134 patients with cT1bRMs, 297 were initiated on surveillance (26%), including 207 (70%) with solid, 47 (16%) with Bosniak III/IV, and 43 (14%) with indeterminate lesions. In a multivariable analysis, the predictors of surveillance included Charlson Comorbidity Index ≥2 versus 0 (odds ratio [OR] 1.43, 95% confidence interval [CI] 0.97-2.13), nonsolid tumor type (Bosniak III/IV cyst: OR 8.03, 95% CI 4.58-14; indeterminate: OR 5.42, 95% CI 2.86-10.3), and benign findings on a renal mass biopsy (OR 24.0, 95% CI 9.07-63). For the 297 surveilled cT1bRM patients, the cumulative incidence of DI at 2 yr was 27%, and the rates of MFS, CSS, and OS were, respectively, 91%, 96%, and 84% at 3 yr after initiating surveillance. A subset analysis excluding cystic, indeterminate, and biopsy-proven benign tumors found the cumulative incidence of DI at 2 yr to be 35%, with MFS and OS rates to be 95% and 78%, respectively, at 3 yr. In a multivariable analysis, initial surveillance was not associated with OS (vs immediate treatment; hazard ratio [HR] 1.47, 95% CI 0.83-2.63), with age as the only significant factor (HR 1.31, 95% CI 1.16-1.48). Limitations include the study's observational and retrospective nature. Conclusions and clinical implications: The MUSIC data support active surveillance for select patients with cT1bRMs. Patient summary: In this report, we looked at the outcomes of surveilling larger (cT1b) renal masses in a large population in Michigan. We found that watching instead of treating cT1b renal masses immediately in older people with more medical conditions did not change survival or cause the cancer to spread compared with people who were treated immediately. We conclude that surveillance for cT1b cancer is an option that should be considered for all patients but implemented selectively.