Finelli A, Cheung DC, Al-Matar A, et al. - In this study, the growth rates and progression of different histologic subtypes of renal cell carcinoma small renal masses (SRM^RCC) were compared in the largest cohort of patients with biopsy-characterized SRMs on AS. Researchers combined data from patients in a multicenter Canadian trial and a Princess Margaret cohort to include 136 biopsy-proven SRM^RCC lesions managed by AS, with treatment deferred until progression or patient/surgeon decision. They characterized tumor progression by sustained size ≥ 4 cm or volume doubling within 1 yr. The results exhibited that tumor growth varies between histologic subtypes of SRM^RCC and among SRM^RCC, which likely reflects individual host and tumor biology. The data revealed that initial follow-up of histologically characterized SRMs can inform personalized treatment for patients on AS, without validated biomarkers that predict this variation,