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, "ghosta" or "shadowa" 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.