Mammary invasive micropapillary carcinoma in a male cat: Immunohistochemical description and clinical follow-up.

We describe the case of a 14-year-old Domestic Short Hair male cat that presented with a single mammary tumour one centimetre in diameter, classified as invasive micropapillary carcinoma. Histology and immunohistochemistry revealed a high mitotic index, a KI-67 index of 10%, a lack of reactivity to myoepithelial markers, and a dense infiltration with T and B lymphocytes at the periphery of the tumour. Micrometastases were detected in the regional lymph node at the time of surgery. Overall survival time was 10 months with a disease-free interval of 7.5 months. Distant metastases in the sublumbar lymph nodes confirmed the aggressiveness of this tumour, which has recently been subtyped in female cats. This is the first case reported in male cats with a complete follow-up, highlighting the importance of prompt and aggressive treatment in the presence of mammary tumours in male cats.