Malignant Pilomatricoma in 3 Dogs

Malignant pilomatricoma, also known as pilomatrix carcinoma and calcifying epitheliocarcinoma (in the human literature), has been considered a rare neoplasm of dogs. The authors present 3 canine cases of malignant pilomatricoma (2 with distant metastasis) and compare its behavior with reported behavior. Cases include an 8-year-old spayed female Airedale Terrier, a 7-year-old male Bassett Hound, and a 12-year-old intact male Giant Schnauzer. In all cases, the histologic features included trabeculae of basaloid cells, abrupt keratinization, “ghost” or “shadow” cells, and various features of malignancy consistent with a diagnosis of malignant pilomatricoma. Metastasis, including that to bone, was confirmed in 2 cases. Four cases of the 13 canine pilomatricomas diagnosed within a 24-month period (2006–2008) at the Ohio State University (2 of which are discussed in this report) were classified as malignant, which suggests that malignant pilomatricoma is more common than previously reported.