Introduction:

Metastatic risk for small renal mass (SRM) patients on active surveillance (AS) is low and often outweighed by treatment morbidity/mortality.  Current AS literature is confounded by highly selected SRM patients who are unfit for treatment, hence neither treatment rates nor standardized progression criteria for triggering treatment in healthier SRM patients are well defined. We report our initial experience with a novel SRM management approach that includes: 1) universal AS recommendation for all SRM patients without progression at presentation, and 2) AS management using specific prospectively applied progression criteria for triggering treatment recommendation.

Methods:

All non-end stage renal disease patients with enhancing SRM tumors and no prior renal cell carcinoma (RCC) history who presented from January 2013 to January 2017 to a single urologic oncologist at a National Comprehensive Cancer Network institute were recommended AS if pre-defined progression criteria were not met at presentation. Progression criteria for recommending treatment at presentation or during AS were the absence of benign tumor biopsy histology + presence of any of the following: longest tumor diameter (LTD) >4 cm; growth rate >5 mm/year; LTD >3 cm + growth rate ≥3 mm/year; high risk biopsy histology; >cT3a stage; or symptoms. SRM biopsy was recommended for LTD >2 cm. The primary outcome measure was 1 and 3-year progression-free survival (PFS); the secondary outcome measure was metastasis-free survival (MFS).

Results:

Of 127 SRM patients with >3 months follow up, 4 met progression criteria at presentation and were recommended treatment. All remaining 123 SRM patients (median initial LTD 2.2, range 0.9-3.9 cm) were managed with initial AS. Median follow up for these 123 AS patients was 30 (range 6-68) months, during which 35 (29%) met at least 1 progression criterion. 1 and 3-year PFS rates were 92%, and 70%, respectively. Shorter PFS was associated with initial LTD (3-year PFS 83%, 75%, 45% for <2 cm, 2.1-3 cm, >3cm, respectively) and clear cell RCC biopsy histology (3-year PFS 45%). Most (28/35; 80%) progressing patients converted to treatment (27 surgery, 1 ablation). Only 1/88 (1%) non-progressing patients converted to treatment for anxiety or other causes. Benign tumor resection incidence was 0%, and most (61%) resected tumors had adverse RCC pathology (high grade and/or pT3a). MFS for progressing or non-progressing patients was 100%.

Conclusion:

Universal initial AS for SRM patients using these specific progression criteria significantly delays or avoids treatment for most patients with initial LTD <3 cm, and overall improves identification of aggressive vs. indolent tumors for treatment selection by avoiding benign tumor removal and enriching resection for adverse RCC pathology. Longer PFS and MFS rates are needed to better assess the durability and oncologic safety of universal AS.

Funding: NA