Extended Duration of Active Surveillance of Small Renal Masses: A Prospective Cohort Study

Purpose:We report the natural history of small renal masses in patients undergoing active surveillance with extended followup.Materials and Methods:We performed a prospective cohort study in patients undergoing active surveillance of small renal masses diagnosed between 2001 and 2011 at a single institution. All patients underwent active surveillance of small renal masses presumed to be renal cell carcinoma based on diagnostic imaging. Reported patient outcomes included progression to treatment, metastatic disease and/or death. Linear and volumetric tumor growth rates were evaluated.Results:Included in study were 103 patients with a total of 107 small renal masses. Median followup was 55.5 months in patients who continued on active surveillance. Median maximum diameter and volume at diagnosis were 2.1 cm (IQR 1.5-2.7) and 4.8 cm³ (IQR 1.7-11.9), respectively. At last followup 53 patients (51.5%) were alive without metastatic disease, 48 (45.6%) had died of another cause and metastatic disease had developed in 2 (1.9%), including 1 (1.0%) who ultimately died of metastatic renal cell carcinoma. The mean ± SEM linear and volumetric growth rates of all small renal masses were 0.21 ± 0.03 cm per year and 6.15 ± 2.15 cm³, respectively. Study limitations include nonstandardized followup and a lack of biopsy data on most patients.Conclusions:During extended followup the majority of small renal masses in patients on active surveillance display indolent behavior. The risk of progression to metastatic disease remains low.