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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.

Early histologic changes in lesions at vaccine sites were compared in cats, mink, and ferrets. Twenty-four 4-month-old cats, 20 4-month-old mink, and 20 12-month-old ferrets were vaccinated with three rabies virus vaccines, two feline leukemia virus vaccines, alum adjuvant, and saline. Injection sites were excised at selected time points up to 21 days postvaccination. Histologic examination of the tissue revealed significant differences among the cats, mink, and ferrets in the local response to the commercial vaccines. When compared with ferrets and mink, cats had more lymphocytes in response to all three rabies vaccines. Production of fibroblasts, collagen, and macrophages differed among the three killed aluminum-adjuvanted vaccines in cats but did not differ significantly in mink or ferrets. Cats produced fewer binucleate cells than did mink or ferrets in response to the two adjuvanted leukemia virus vaccines. Differences seen in early tissue response of cats to commercial vaccines may be related to the increased predisposition of cats to vaccine-associated sarcomas.