Cutaneous Pilomatrical Carcinosarcoma in a Dog.

Malignant pilomatricomas are uncommon cutaneous neoplasms in veterinary and human medicine. Pilomatrical carcinosarcoma is a rare subset of malignant pilomatricoma that has been described in man. This article reports a neoplasm with morphological features of pilomatrical carcinosarcoma in a dog. The nodular neoplasm occurred on the left lateral hock and was partially alopecic. Microscopically, the tumour was composed of a cystic carcinomatous component surrounding areas of abrupt keratinization and a sarcomatous component exhibiting bundles of spindle cells and irregular, scalloped areas of mineralized and non-mineralized osteoid matrix. The carcinomatous and sarcomatous areas were immunoreactive for pan-cytokeratin and vimentin, respectively, while immunoreactivity for e-cadherin was restricted to the carcinomatous component of the neoplasm. The unique morphological features of this tumour were similar to those described in human pilomatrical carcinosarcoma.