Immunohistochemical Profile of 20 Feline Renal Cell Carcinomas.

Renal cell carcinoma (RCC) is uncommon in cats, but makes up the majority of epithelial neoplasms in the kidney. The immunohistochemical profile of 20 feline RCCs (13 tubular carcinomas, four tubulopapillary carcinomas, one papillary carcinoma and two anaplastic carcinomas) was evaluated. Primary antibodies used were specific for Pax8, KIT, CD10, cytokeratins and vimentin. A polymer-based immunoperoxidase procedure was used. Nineteen tumours (95%) expressed Pax8; 12 (60%), KIT; 15 (75%), CD10; 20 (100%), cytokeratins; and 19 (95%), vimentin. Nuclear Pax8 immunoreactivity was readily apparent, but variation in labelling intensity was present within a given section. KIT reactivity was diffuse, cytoplasmic and relatively homogeneous. CD10 immunoreactivity was predominantly membranous along the apical border of tubular epithelial cells and was less commonly cytoplasmic. CD10 immunoreactivity was less intense in areas with papillary differentiation and absent in solid areas. Cytoplasmic cytokeratin expression was strong in 18 tumours and weak in two; the papillary portion of one tumour had distinct submembranous expression. Vimentin immunoreactivity, which ranged from diffuse to focal, was difficult to evaluate due to strong stromal immunoreactivity and its patchy expression in phenotypically similar neoplastic cells. Fewer non-renal tumours were positive for Pax8 than for CD10. Considering overall sensitivity and specificity, Pax8 appears to be a valuable marker for distinguishing feline tumours arising in the kidney from other neoplasms.