Coexisting Hybrid Malignancy in a Solitary Sporadic Solid Benign Renal Mass: Implications for Treating Patients Following Renal Biopsy

Abstract

INTRODUCTION AND OBJECTIVES Concern regarding coexisting malignant pathology in benign renal tumors deters renal biopsy and questions its validity. We examined rates of coexisting malignant and high grade pathology in resected benign solid solitary renal tumors. METHODS Using our prospectively maintained database we identified patients with solitary solid renal tumors who underwent surgical resection between 1994 and 2012 (n=1829). Lesions containing elements of renal oncocytoma (RO), angiomyolipoma (AML) or other benign pathology formed the basis for this analysis. Patients having an oncocytic malignancy, without presence of a classic oncocytoma, and those with known hereditary syndromes were excluded. RESULTS 147 patients with pathologically proven elements of RO (n=96), AML (n=44), and other solid benign pathology (n=7) were identified. Median tumor size was 3.0 cm (IQR 2.2 – 4.5) and tumor anatomic complexity, as quantified by the RENAL NS, was low in 28%, moderate in 56%, and high in 16%. Only 4 patients (2.7%) were documented as having hybrid malignant pathology, all involving low grade chromophobe RCC in the setting of RO. After a median follow-up of 44 (IQR 33 – 55) months, no patients with hybrid tumors experienced regional or metastatic progression. CONCLUSIONS In our cohort of patients with a solitary, sporadic, solid benign renal mass, <3% of tumors exhibited coexisting hybrid malignancy. Importantly, no patients harbored coexisting high grade pathology. These data suggest that uncertainty regarding hybrid malignant pathology coexisting with benign pathologic components should not deter renal biopsy, especially in the elderly and comorbid.

Utility of fine‐needle aspiration and core biopsy with touch preparation in the diagnosis of renal lesions

“…Also, certain diagnostic groups are difficult to diagnose in small specimens, especially classifying an oncocytic neoplasm as oncocytoma versus oncocytic/eosinophilic variants of chromophobe and clear cell RCC, respectively . Hybrid tumors have been described with mixed morphology of renal oncocytoma and chromophobe RCC, and chromophobe RCC, especially the oncocytic variant, may focally resemble renal oncocytoma . The 4 cases in our series diagnosed as oncocytoma did not have corresponding surgical specimens for confirmation, and were diagnosed on CB by morphology and immunohistochemistry with or without special stains.…”

“…10,22 Hybrid tumors have been described with mixed morphology of renal oncocytoma and chromophobe RCC, and chromophobe RCC, especially the oncocytic variant, may focally resemble renal oncocytoma. [33][34][35] The 4 cases in our series diagnosed as oncocytoma did not have corresponding surgical specimens for confirmation, and were diagnosed on CB by morphology and immunohistochemistry with or without special stains. It has been recently suggested that oncocytic neoplasms are signed out as "renal oncocytic neoplasm" on small biopsies because RCC may uncommonly show focal areas resembling renal oncocytoma and due to the tumor heterogeneity of hybrid tumors.…”

Renal Mass Biopsy in the Era of Surgical Alternatives

“…Classically, hybrid renal tumors have been seen as part of the renal syndrome of Birt-Hogg-Dube or in renal oncocytosis, but they can be seen sporadically [47]. In a retrospective study of 147 solitary solid renal masses classified as benign or oncocytic, 3 % showed a coexisting hybrid malignancy [48].…”

MRI Phenotype in Renal Cancer

“…In addition, some hybridrenal lesions may contain distinct regions of both oncocytoma and RCC within it, thereby being prone to sampling error even if the obtained tissue is confidently interpreted by the pathologist. 108 Given these pitfalls, we suggest that, even when a renal mass biopsy returns a diagnosis of oncocytoma, continued imaging surveillance should be pursued to ensure continued stability.…”