Active Surveillance of Biopsy-Confirmed Oncocytic Renal Tumors: Growth Dynamics and Impact on Renal Function.

Abstract

Oncocytic neoplasms account for up to 15% of small renal masses. Active surveillance (AS) is increasingly adopted for these lesions; however, knowledge gaps remain regarding their growth kinetics, concordance with renal tumor biopsy, and impact on renal function. This study reviews these factors in the largest cohort of biopsy-confirmed oncocytic neoplasms managed with AS. This single-center, retrospective study included patients with biopsy-confirmed oncocytoma or chromophobe renal cell carcinoma (chRCC) on AS (2003-2021). Tumor growth rates and change in renal function (estimated glomerular filtration rate) were analyzed using linear mixed models, while development of chronic kidney disease was assessed using Cox proportional hazards model. Biopsy-to-surgical pathology concordance and triggers for intervention were examined. Among 229 patients (245 lesions; 222 oncocytomas, 23 chRCC), the median time between first and last imaging was 4.7 and 2.5 years, respectively. Predicted growth rates were 0.21 cm/y (oncocytoma) and 0.31 cm/y (chRCC). Larger baseline tumor size correlated with faster growth (<i>P</i> = .04), while age inversely correlated with growth rate (<i>P</i> < .01). Intervention was more common in the chRCC cohort (35% vs 13%). Biopsy-to-surgical pathology concordance rates were 80% for oncocytoma and 86% for chRCC. No significant association was found between tumor size and renal function decline (<i>P</i> = .3) or level (<i>P</i> = .6). There were no events of metastases or kidney cancer-related deaths over a median follow-up of 5.7 years (IQR: 3.0, 8.7). Oncocytic lesions on AS demonstrate slow growth, low intervention rate, preservation of renal function, and excellent disease-specific survival. Although biopsy limitations exist, histology-guided AS provides effective management.