Active surveillance for renal masses up to 2 cm: long-term oncological outcomes from a prospective multi-institutional study

Purpose The widespread use of cross-sectional imaging has increased the incidental detection of small renal masses (SRMs). In this context, overtreatment represents a major concern, particularly for lesions < 2 cm. Most evidence derives from retrospective registries, whereas prospective data remain limited. Methods This multi-center, prospective, non-randomized clinical trial was conducted in five European centers between January 2015 and July 2021. Seventy-six patients aged > 50 years with asymptomatic, unilateral SRM < 2 cm were enrolled and followed under a structured prospective active surveillance (AS) protocol with periodic axial imaging. Active treatment was recommended according to predefined progression criteria or patient preference. The primary endpoint was event-free survival (EFS); secondary endpoints included treatment-free survival (TFS), overall survival (OS), and cancer-specific mortality (CSM). Results 69 patients were included in the analyses. After a median follow-up of 88 months, 8-year EFS and TFS were 66% and 83%, respectively. 17% of patients required active treatment, mainly due to tumor growth. The 8-year OS and CSM were 88% and 9.6%. One patient died of metastatic RCC. Shorter tumor doubling time (DT) (< 12 years) and high RENAL score were significantly associated with higher risks of event and treatment. Endophytic tumors, and higher PADUA score also predicted adverse outcomes. Conclusion Long-term follow-up confirms AS as the standard initial option for selected patients with SRMs <= 2 cm, with a low rate of progression and optimal survival rates. Tumor DT and mass location should be considered in clinical decision-making to identify patients who will deserve a deferred treatment in case of progression.