57: Modeling Longitudinal Renal Function of Small Renal Mass Patients on Active Surveillance

Background: Active surveillance (AS) is increasingly utilized to manage patients with small renal masses (SRM). Our understanding of renal function decline in patients on AS is limited by inconsistent follow-up and variable timing between renal function tests. We describe AS patients' longitudinal data on chronic kidney disease (CKD) stage progression.

Methods: We performed a retrospective study using an institutional database to identify patients diagnosed with a SRM and placed on AS from 2016 to 2022. Demographic, clinical, and radiological data were collected. Baseline renal function, as well as renal function at 6 months, 12 months, and 24 months from diagnosis, were used to interpolate the probability of CKD stage progression.

Results: Our cohort included 111 patients with a median age of 65 years (IQR 54-73), initial tumor diameter of 2.2 cm (1.6-2.8), nephrometry score of 6 (5-8), and Charlson Comorbidity Index of 5 (4-7). Forty-four masses were biopsied; 27% (12) were clear cell carcinoma and 14% (6) were papillary renal carcinoma. Seventeen patients progressed to intervention; 8 patients were managed with partial nephrectomy, 2 patients with radical nephrectomy, and 7 patients with ablation. One patient developed metastasis and 7 patients died of other causes. Median follow-up was 18.9 months (IQR 9.9-47.9). At 1-year, 9.6% of patients had a 30% decline in eGFR. Table 1 contains CKD stage progression for this cohort. Patients presenting with CKD stages 1 to 2 have a high probability of remaining stable, while patients with a CKD ≥ stage 3a have a higher risk of progressing to later stages in the first 2 years of AS.

Conclusions: The risk of CKD stage progression in AS patients is higher when baseline renal function impairment is greater. Our findings suggest a need for more intensive monitoring and management of patients with baseline CKD ≥ stage 3a.