Basal cell tumors are common skin masses found in dogs and cats. Basal cell tumors originate from the deepest layer of skin called the basal epithelium. These masses can vary in size from a few mm to as large as 3 cm. They are typically well circumscribed, round, raised masses that can be red purple or blue in color. In cats, basal cell tumors are commonly heavily pigmented, appearing brown or black in many cases.
Basal cell tumors can be benign in nature (not cancerous) or malignant (cancerous). The malignant variety is significantly more common in cats than dogs. Metastasis, or spread to other tissues, is rare.
Diagnosis of basal cell tumors occurs by hallmark characteristics on physical examination, as well as fine needle aspirate of the lesion, followed by microscopic analysis of the cells on a slide. If a typical cellular pattern consistent with basal cell tumor is noted, then surgical removal is recommended. Since benign versus malignant characteristics on fine needle aspirate are not always clear, I always recommend complete excision of these tumors, followed by histopathology of the mass to check for surgical margins and confirm the diagnosis.
Whether the mass is found to be malignant or benign, complete surgical excision is curative in the majority of cases.
Roger L. Welton, DVM
Founder and Chief Editor, Web-DVM.net
President, Maybeck Animal Hospital
Article updated 11/11/2012