Mammary carcinoma in a male cat following long-term medroxyprogesterone acetate treatment: case report and review of the literature.

In male cats, as in men, mammary carcinomas are rarely reported. However, like in females, hormonal therapy is a significant risk factor. This study reports the case of an 11-year-old male cat with multiple mammary tumours and a history of long-term medroxyprogesterone acetate therapy for the suppression of sexual behaviour, along with a brief review of the literature. Complete surgical removal of the right mammary chain and the ipsilateral inguinal lymph nodes was performed, and all tissues were submitted for histology. Histological examination revealed the presence of a tumour in the third and fourth mammary glands, consisting of neoplastic cells arranged in various structures, including tubulopapillary and tubular structures, sometimes cystically dilated, and solid areas. The inguinal lymph nodes were also involved. The morphology was consistent with a diagnosis of mammary carcinoma, tubulopapillary type, with nodal metastases. Immunohistochemistry revealed that tumour cells were positive for cytokeratin (clones AE1/AE3), while stromal cells were positive for vimentin (clone V9). The proliferation marker Ki-67, evaluated on both the primary tumour and the nodal metastases, was strongly expressed in the nuclei of neoplastic cells, with a Ki-67 proliferation index of 8.9% and 20% for the primary tumour and the metastases, respectively. This case highlights the importance of considering the possibility of malignant mammary tumours not only in female but also in male cats with a history of long-term hormonal treatment for suppression of sexual behaviour.