Pseudoangiomatous squamous cell carcinoma in the oral cavity of a dog.

An 8-year-old, spayed, female Labrador Retriever mixed-breed dog was presented to the Cornell University Hospital for Animals with an invasive oral mass involving the upper left fourth premolar and first molar teeth. Initial biopsy results suggested a poorly differentiated squamous cell carcinoma, whereas further histologic examination of the surgically removed mass revealed a hemangiosarcoma-like mass composed of numerous vascular clefts and variable numbers of keratinizing epithelial cells. Histologic and immunohistochemical characteristics were compatible with pseudoangiomatous squamous cell carcinoma, a well-recognized human variant of acanthomatous squamous cell carcinoma. Because of histomorphologic similarities with canine gingival hemangiosarcoma, diagnosticians should be aware of the present tumor variant as a differential diagnosis for vascular-like growths in the oral cavity of dogs.