Histological and immunohistochemical features of a feline sarcomatoid renal cell carcinoma

Sarcomatoid renal cell carcinoma (SRCC) is a rare and poorly characterized neoplasm in domestic animals. This report describes the clinicopathological and immunohistochemical findings of SRCC in a 7-year-old male Domestic Shorthair cat presenting with progressive weight loss, azotaemia and right-sided renomegaly. At necropsy, the right kidney was diffusely enlarged and replaced by a firm, pale-tan, poorly demarcated mass. Histologically, the renal parenchyma was effaced by a pleomorphic neoplasm composed of polygonal, spindle-shaped and multinucleated cells arranged in irregular cords and bundles. Immunohistochemically, all neoplastic cell populations were strongly positive for vimentin and labelled variably for cytokeratin AE1/AE3, while spindle and multinucleated cells also labelled for ionized calcium-binding adaptor molecule 1 (Iba-1). Anti-smooth muscle actin labelled strongly in spindle cells, whereas antibodies to CK7, high molecular weight cytokeratin, Melan A, p63 and uroplakins II and III failed to label. Based on morphological and immunophenotypic features, the tumour was diagnosed as a SRCC. The histological and immunohistochemical patterns observed closely resemble those described in human SRCC, reinforcing the comparative value of this entity. This report expands the limited knowledge of feline SRCC and highlights the importance of a focused immunohistochemical panel comprised of antibodies to vimentin, cytokeratin AE1/AE3 and Iba-1 for the accurate diagnosis of undifferentiated renal neoplasms in cats.