Hybrid oncocytic/chromophobe renal cell tumours do not display genomic features of chromophobe renal cell carcinomas

Hybrid oncocytic/chromophobe tumours (HOCT) are renal tumours recently described displaying histological features of both renal oncocytoma (RO) and chromophobe renal cell carcinoma (ChRCC), raising the question of their precise signification in the RO/ChRCC group. This study aimed to describe clinicopathological features of so called HOCT and to characterise their genomic profile. Five hundred and eighty-three tumours belonging to the ChRCC/RO group were retrospectively reviewed. Twelve tumours that could not be classified as RO or CHRC were considered as HOCT. Hale staining and cytokeratin 7 (CK7) immunostaining were performed. Genomic profile was established by array comparative genomic hybridisation (array-CGH) on frozen samples. Mean age at diagnosis was 70 years (range 46-83). No recurrence was observed (median follow-up: 18 months; range 9-72). Tumour size ranged from 1 to 11 cm. HOCT showed an admixture of RO- and ChRCC-like areas and/or hybrid cells with overlapping cytonuclear and/or histochemical features. Hale staining was apical in 50 to 100 % of cells, and CK7 was expressed in 10 to 100 % of cells. Genomic profile was balanced in seven cases or showed a limited number of random imbalances in five cases, as observed in RO. In no instances were observed the characteristic chromosome losses of ChRCC. These results suggest that so called HOCT are not true hybrid tumours and rather could represent a morphological variant of RO. From a diagnostic perspective, an array-CGH analysis could be performed in ambiguous ChRCC/RO cases to formally exclude the diagnosis of ChRCC.