Mammary Carcinoma with Peritoneal Metastasis in a Cow

cuboidal epithelial cells with well-developed apical microvilli and oval vesicular nuclei. The cytoplasm and tubular lumens of both the primary tumor and the metastatic nodules con­ tained periodic acid-Schiff-positive material, which was re­ sistant to diastase digestion. This was more pronounced in the metastatic tumor than in the primary tumor. Metastasis of mammary tumors is not common, even in the dog. In a study of424 canine mammary tumors, Cotchin­ diagnosed 187 malignant tumors, of which only 41 metas­ tasized. A review of the literature of canine mammary car­ cinomas found that ofthose that had proven metastases, the percentage of involvement ofdifferent organs was as follows: lymph nodes 64%, lungs 53%, liver 13%, kidney II %, heart II %, and bone 10%.6 There are too few cases of bovine mammary carcinoma to determine the expected pattern of metastasis. Of the ten cases of bovine mammary carcinoma reported in the literature, six metastasized to the lymph nodes. L7 Of these six cases, one had metastasis to the lungs, a second case had metastasis to the lungs, liver, and dia­ phragm, and a third case spread to the lungs, pleura, peri­ cardium, and kidney. Peritoneal metastasis was not men­ tioned in any of the bovine cases. Implantation of tumors on serosal surfaces is more com­ mon in cases of cholangiocellular carcinoma, ovarian car­ cinoma, bovine and ovine intestinal carcinoma, and equine gastric squamous cell carcinoma.' Because of the extensive serosal implantation of the tumor, in this case a differential diagnosis considered was peritoneal mesothelioma with con­ comitant mammary carcinoma. This possibility was ruled out by the histologic similarity of the tumors in both the mammary gland and the peritoneal cavity, and the presence of periodic acid-Schiff-positive diastase-resistant material within the tubular lumens of the peritoneal tumor.' Due to the rare occurrence of mammary tumors in cows, the risk factors and the biological behavior of bovine mam­ mary carcinoma are virtually unknown. This is in sharp con­ trast to the high rate of human mammary carcinoma (any carcinoma arising in the glandular and ductular structures of the breast). Epidemiological data support a role for hyper­ estrinism in the genesis of human breast cancer. 8 Pregnancy shortens such exposure to estrogen. The low rate of mam­ mary carcinoma in cattle may be partially due to the high rate of pregnancy in this species. Estrogen levels were not determined in this cow, so that theory cannot be addressed in this case. However, this case description augments the few cases ofbovine mammarycarcinoma that have been reported and assists in the future discernment of the biological be­ havior of this rare neoplasm.