Clear-cell papillary renal cell carcinoma: 24 cases of a distinct low-grade renal tumour and a comparative genomic hybridization array study of seven cases.

AIMS: To report clinicopathological and genomic characteristics of (ccpRCC), a rare, recently characterized renal tumour entity. METHODS AND RESULTS: Twenty-four renal tumours identified as ccpRCC were collected. Data from comparative genomic hybridization on microarrays (array-CGH) were obtained for seven of these. Most tumours (58%) occurred in the absence of renal disease. Mean patient age was 58.1 years. Tumours were small (mean size: 2.4 cm) and classified as pT1. Histological characteristics consisted of tubules and papillae lined by a single layer of small clear cells harbouring low-grade nuclei (Fuhrman grades 1 or 2). Architectural variations, with compact areas (41% of cases) and a micro- or macrocystic pattern (67% of cases) were observed frequently. Immunostaining demonstrated diffuse, strong expression of cytokeratin 7 and vimentin, whereas CD10, racemase, RCC antigen, translocation factor E3, TFE3 and translocation factor EB were consistently negative. In seven tumours, array-CGH detected no chromosomal imbalances. CONCLUSIONS: Clear-cell papillary renal cell carcinoma (ccpRCC) were differentiated from other renal neoplasms by a specific constellation of histopathological and immunohistochemical features, without characteristic genomic imbalances. Clinical, histopathological and genomic data suggested that these tumours have a low potential for malignancy.