Coexisting hybrid malignancy in a solitary sporadic solid benign renal mass: implications for treating patients following renal biopsy

Purpose: Concern regarding coexisting malignant pathology in benign renal tumors deters renal biopsy and questions its validity. We examined the rates of coexisting malignant and high grade pathology in resected benign solid solitary renal tumors.

Materials and methods: Using our prospectively maintained database we identified 1,829 patients with a solitary solid renal tumor who underwent surgical resection between 1994 and 2012. Lesions containing elements of renal oncocytoma, angiomyolipoma or another benign pathology formed the basis for this analysis. Patients with an oncocytic malignancy without classic oncocytoma and those with known hereditary syndromes were excluded from study.

Results: We identified 147 patients with pathologically proven elements of renal oncocytoma (96), angiomyolipoma (44) or another solid benign pathology (7). Median tumor size was 3.0 cm (IQR 2.2-4.5). As quantified by the R.E.N.A.L. (radius, exophytic/endophytic, nearness to collecting system or sinus, anterior/posterior and location relative to polar lines) nephrometry score, tumor anatomical complexity was low in 28% of cases, moderate in 56% and high in 16%. Only 4 patients (2.7%) were documented as having hybrid malignant pathology, all involving chromophobe renal cell carcinoma in the setting of renal oncocytoma. At a median followup of 44 months (IQR 33-55) no patient with a hybrid tumor experienced regional or metastatic progression.

Conclusions: In our cohort of patients with a solitary, sporadic, solid benign renal mass fewer than 3% of tumors showed coexisting hybrid malignancy. Importantly, no patient harbored coexisting high grade pathology. These data suggest that uncertainty regarding hybrid malignant pathology coexisting with benign pathological components should not deter renal biopsy, especially in the elderly and comorbid populations.