Syed JS, et al. - In patients with renal cell carcinoma (RCC), the risks of contralateral tumor development were assessed using the Surveillance, Epidemiology, and End Results database. Participants were patients with a metachronous, contralateral RCC diagnosed ≥1 year after primary diagnosis. Links between clinicopathologic factors and metachronous, bilateral RCC were assessed via a competing risks analysis. Researchers calculated cumulative incidence and standardized incidence ratios (SIRs). Of 80,403 identified RCC cases with a median follow-up of 8.3 years, metachronous, contralateral RCC development was reported in 1063 (1.3%) (median of 6 years after diagnosis). Compared to previous reports, a possibly higher cumulative incidence of metachronous, contralateral RCC was reported. Factors that increased the risk of metachronous, contralateral RCC development included younger age, black race, papillary histology, and male sex. In all demographic groups, the observed high SIRs may favor a rationale for lifelong surveillance, especially in high-risk subgroups with early disease onset.