Piloleiomyosarcoma in cats: Histological and immunohistochemical features

This study describes the histomorphology and immunohistochemical profile of 9 cases of feline piloleiomyosarcoma. Cats ranged in age from 7 to 16 years (mean 10), and tumors were 7 to 24 mm in diameter (mean 15). Tumors were composed of fusiform cells that were haphazardly arranged or in variably sized interwoven bundles. Neoplastic cells had eosinophilic and fibrillar cytoplasm, and elongated blunt-ended nuclei. Entrapment of hair follicles and absence of vascular components support an origin from the smooth muscle cells of the arrector pili. Additional findings included bizarre nuclei and giant cells (7/9 cases), atypical mitoses (7/9 cases), ulceration (3/9 cases), and intratumoral necrosis (6/9 cases). Neoplastic cells expressed calponin, desmin, α-smooth muscle actin, and vimentin, but not CD18, CD31, cytokeratins, glial fibrillary acidic protein, neuron-specific enolase, Melan A, p63, or S-100 protein. Surgical excision was curative in 6/9 cases, with local recurrence in 2/9 cases and metastasis to local lymph nodes in 1/9 case. Clinical outcome was influenced by mitotic count, infiltration of subcutaneous tissue, and intensity of nuclear immunolabeling for p53.