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Dogs with ovarian papillary adenocarcinoma occasionally present with ascites and/or pleural effusion. These aspirated fluids often contain a large number of cells, and distinction between neoplastic cells and activated mesothelial cells can be difficult. In this study, 7 cases of canine ovarian papillary adenocarcinoma, including 3 with ascites and pleural effusion, were immunohistochemically examined. Ovarian tumor cells were positive for cytokeratin CAM5.2 (CAM5.2), Wilms' tumor 1 (WT-1) and progesterone receptor (PR) in all 7 cases. A metastatic lesion of the mediastinum in one case was also positive for CAM5.2, WT-1 and PR. Immunohistochemistry on cell blocks obtained from ascites and/or pleural effusion of 2 cases revealed the presence of PR-positive epithelial cells. Whereas, activated mesothelial cells in ascites or pleural effusion collected from dogs without neoplastic lesions were negative for PR. In addition, surface epithelium and subsurface epithelial structures (SES) of normal canine ovaries, that are considered to be the cell of origin for ovarian papillary adenocarcinoma, were also positive for CAM5.2, WT-1 and PR. These results indicate that, together with CAM5.2, WT-1 and PR is a useful diagnostic marker for canine ovarian papillary adenocarcinoma. Expression of PR may be associated with progesterone-dependent nature of canine ovarian papillary adenocarcinoma.

A female golden retriever was referred to assess a history of a palpable abdominal mass. A serum chemistry analysis revealed elevated concentrations of blood urea nitrogen, creatinine, calcium, and parathyroid hormone-related protein (PTH-rP). Exploratory laparotomy revealed an ovoid mass within the right ovary. This mass was removed surgically by performing an ovariohysterectomy. The right ovarian mass was diagnosed as a serous papillary adenocarcinoma. Following surgery, the dog recovered, and the serum calcium and PTH-rP concentrations decreased. Therefore, concentrations of PTH-rP and calcium might be associated with serous papillary adenocarcinomas. Serial evaluation of the serum PTH-rP and calcium was useful for evaluating the prognosis.