Noninvasive malignant mammary adenomyoepithelioma in a male cat

This report describes the histopathological and immunohistochemical findings of a noninvasive malignant mammary adenomyoepithelioma in a seven-year-old neutered male mixed-breed cat. The animal was euthanized due to an extensive mandibular fracture caused by squamous cell carcinoma. Macroscopically, a 3 × 1.5 cm, elevated, well-defined, ulcerated, lobulated, reddish-white, solid – occasionally cystic – and firm nodule was observed in the right inguinal mammary gland. Microscopically, an expansive neoplastic proliferation composed of myoepithelial and epithelial cells arranged predominantly in a papillary pattern was observed. Immunohistochemistry was performed for the markers C-Kit, pan-cytokeratin (CK-AE1/AE3), cytokeratin 7 (CK7), P63, estrogen receptor (ER), progesterone receptor (PR), Ki67, cyclooxygenase-2 (Cox-2), and GATA3. The neoplastic cells were positive for CK AE1/AE3 and 7 (epithelial cells), P63 (myoepithelial cells), Cox-2 (epithelial and myoepithelial cells), and PR (epithelial cells). Positive results for CK-AE1/AE3, CK7, and P63 confirmed the epithelial and myoepithelial nature of the tumor, the mitotic index and elevated Ki-67 expression supported the interpretation of a malignant proliferative phenotype and contributed to the classification of the lesion as a noninvasive malignant adenomyoepithelioma. Based on the macroscopic, microscopic, and immunohistochemical findings, a diagnosis of noninvasive malignant mammary adenomyoepithelioma was established.