Introduction:

Active surveillance (AS) is an alternative to primary intervention (PI) in the management of small renal masses (SRMs; clinical stage T1a). However, AS remains underutilized due to a lack of strong, prospective data. One of the barriers to the widespread implementation of AS is the lack of prospectively conducted comparative studies with long-term follow-up. While a randomized trial is not feasible due to the reliance of AS on patient selection, the Delayed Intervention and Surveillance for Small Renal Masses (DISSRM) Registry prospectively enrolls patients with cT1a SRM who elect either AS or primary intervention (PI) through shared-decision making. We herein report mature outcomes results from the world's largest SRM prospective registry.

Methods:

Since January, 2009, the DISSRM Registry has prospectively enrolled patients with SRMs who choose to undergo PI or AS. The protocol is available at ClinicalTrials.gov (Identifier:NCT02346435). In brief, enrollees are ≥18 years with a clinically localized, solid, enhancing renal mass ≤4.0 cm in diameter (cT1a) on axial imaging. For those on AS, intervention is recommended upon evidence of tumor progression, which is defined as: (1) growth rate (GR) >0.5 cm/year, (2) maximum tumor diameter (MTD) >4.0 cm, or (3) the development of symptoms or (4) metastatic disease. Patients can choose to undergo delayed intervention (DI) or withdraw at any time. Progression-free survival (PFS) was defined as a priori at the inception of the registry based on previous retrospective data and is calculated by evidence of progression (criteria 1-4) or (5) crossover to intervention. Recurrence-free survival (RFS) was defined as freedom from any tumor recurrence (criteria 1-5) or (6) death.

Results:

958 participants enrolled, 377(39.35%) PI and 581(60.65%) AS. Median follow-up was 4.73 years (interquartile range (IQR) 2.13-7.18). Of AS patients, 88 of 581(15.15%) crossed over to DI. PI and AS had similar 12-year cancer-specific survival (CSS) (99.3% vs 99.8%, respectively, log-rank P=0.43). Overall survival was higher in PI patients compared to AS at 3- (97.6% vs 92.9%), 6- (92.8% vs 81.2%), 9- (88.0% vs 63.7%), and 12-years (41.6% vs 57.9%) log-rank P<0.001. Median overall GR was 0.11 cm/year (IQR 0-0.33 cm/year), and 183 experienced progression events. PFS was 84.3% at 3-years, 78.2% at 6-years, 77.3% at 9-years. Crossover rate is 15.16% (88/581), differing significantly with tumor size: <2 cm;10.28% (11/107), 2 to <3 cm;16.25% (26/160); and ≥3 cm; 25.76% (51/198). RFS was not different between PI and DI (P=0.24).

Conclusion:

With fourteen years of experience, the present analysis provides the world's largest prospective comparison of PI to AS with or without DI. Given the absence of a randomized trial, DISSRM demonstrates the best available evidence on appropriateness of AS for cT1a renal masses and confirms suggestions of earlier reports that AS is non-inferior to PI as an initial management strategy. Additionally, the study provides an opportunity to refine the historical approach to AS, including criteria for crossover to intervention. A priori definitions of progression, including GR, do not foretell biological outcomes including adverse pathology, recurrence, or CSS, but prompt increased rates of DI with increasing GR. Increasing tumor size at enrollment and throughout AS predicts DI and biological outcomes including adverse pathology, recurrence, and metastatic progression, and should be considered the primary trigger for DI in patients with an SRM.

Funding: N/A