Uterine adenocarcinoma with peritoneal carcinomatosis in a cat: HBME-1 as a potential marker for uterine epithelial disorders in queens

Uterine adenocarcinomas and the spread of the endometrial neoplastic cells throughout the abdominal cavity (peritoneal carcinomatosis) are rare in cats. The Hector Battifora Mesothelial Epitope-1 (HBME-1) is a widely used monoclonal antibody in human medicine, including uterine disorders, but is scarcely explored in veterinary medicine. Herein, we describe a case of uterine adenocarcinoma with peritoneal carcinomatosis and HBME-1 immunolabeling of the neoplastic cells in a female cat. Clinically, the cat was admitted to a veterinary teaching hospital with fever, and was submitted to ovariohysterectomy after a suspicion of pyometra. The uterus was sent for histopathological analysis, and a diagnosis of uterine adenocarcinoma was made. The animal was euthanized three months after the initial diagnosis, and the cadaver was sent for postmortem examination. At necropsy, there was an irregular-shaped, firm, white, 5 × 3 × 2.5 cm mass in the uterine stump, and multiple 0.3 to 0.7 cm diameter nodules of similar characteristics within the peritoneal cavity. Histologically, the tumors consisted of an infiltrative neoplastic proliferation of epithelial cells arranged in acini and papillae, accompanied by an abundant desmoplastic reaction and marked nuclear and cellular pleomorphism. By immunohistochemistry, the neoplastic cells were reactive for HBME-1, pancytokeratin, progesterone receptor, and estrogen receptor alpha. Additionally, the normal endometrium exhibited apical immunolabeling for HMBE-1. To our knowledge, HBME-1 labeling has never been reported in normal or neoplastic endometrial cells in domestic species. Our findings may expand the application of this antibody in veterinary pathology and broaden the immunohistochemical panel of uterine adenocarcinomas in cats.