Classification of Epithelial Canine Mammary Tumors in a Defined Population

Ductal carcinomas accounted for nearly all metastases seen in epithelial canine mammary tumors submitted to the Tulsa Registry of Canine and Feline Neoplasms in a 4-year period from a defined canine population. Lobular and squamous cell carcinomas were the only other metastatic carcinomas seen. Early ductal carcinoma was used to indicate nonmetastatic ductal carcinoma with a favorable post-surgical prognosis. Benign epithelial tumors were categorized as adenoma, ductal papilloma and squamous cell papilloma. Progressive transformation of well defined adenomas and papillomas to carcinoma was not evident in histologic preparations. Squamous metaplasia was seen in many ductal papillomas and ductal carcinomas. Inclusion of pseudocartilage and pseudoosteoid and osteoid, cartilage and bone with ductal carcinomas, adenomas and ductal papillomas seemed related to secretions escaping from neoplastic epithelial cells into stroma or between proliferating tumor cells. There was proliferation and perhaps even neoplastic transformation of myoepithelial cells in some of these tumors. Changes in myoepithelium, however, appeared to be secondary to neoplastic transformation of epithelium. Bone and cartilage in these tumors were considered heterotopic with no neoplastic potential.