Solid malignant adenomyoepithelioma in the mammary gland of a male dog – first description

Abstract Canine mammary tumors are well known and described in a high frequency in female dogs, and most of them are malignant. However, in male dogs, a very low rate, and benign occurrence seems to be more common. This is the first case report to describe the histologic and immunophenotypic features of a solid malignant adenomyoepithelioma in the mammary gland of a male dog. A sample was received from an intact male dog, Shih Tzu, 12-years-old, for histopathological evaluation. According to clinical history, the mass was located near the prepuce, non-adherent, evolution time unknown. Histologically, the mammary nodule consisted of a neoplastic proliferation of cells in a solid pattern, supported by a scant fibrovascular stroma. Cells had epithelioid form, moderated cytoplasm, lightly eosinophilic, and variably vacuolization. Nuclei are round to ovoid, with occasional karyomegaly and bizarre nuclei. Moderated pleomorphism; high mitotic count. Interspersed with the proliferation, a moderate amount of myxoid matrix production. Immunohistochemical analysis was performed and revealed neoplastic cells positive for p63 (90%), Pan-CK (10%), and PR (75%); HER-2 less than 10%; COX-2 and ER-negative. The results confirmed the diagnosis of solid malignant adenomyoepithelioma. Despite the low occurrence of MGT in male dogs, further studies with a high number of cases are needed. The role of age, breed, sexual status, and hormonal influences is unknown. Understanding the correlation between histological types, their behavior, and immunohistochemistry markers is crucial.