The histological and immunohistochemical features of a metastatic mammary carcinosarcoma in a dog - a case report

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A carcinosarcoma is a tumor composed of cells morphologically resembling both malignant epithelial and mesenchymal components. An 11-year-old, female, mixed-breed terrier was referred to the clinic with complaints of anorexia, vomiting and exercise intolerance. Clinically, tumoral masses were seen in the mammary glands. During necropsy, multilobulated calcified masses were observed in several visceral organs (the liver, kidneys, lungs, small intestines, lymph nodes and thyroid) and both right and left (3rd and 4th) mammary glands. Immunohistochemically, Thyroglobulin, SMA, TTF-1, S100, CD34, and p53 were negative in both epithelial and mesenchymal areas, however, Ki-67 showed high proliferation, especially in the mesenchymal areas. While the positivity of vimentin expression was high in the mesenchymal component of the tumor, the positivity of cytokeratin (CK7 and CK19) expressions was high in the epithelial component of the tumor. In the case of a carcinosarcoma, there is a probability that not only the carcinomatous part, but also the sarcomatous part will metastasize. Despite being uncommon, canine carcinosarcomas should always be considered in the differential diagnosis of mixed mammary tumors, if they include both components. There have not been many previous studies dealing with the metastasis of a mammary carcinosarcoma in dogs as an aggressive tumor. Therefore, we consider this report a worthy contribution and have defined the multiple organ metastasis of a mammary carcinosarcoma.