Damasceno, Karine Araújo “Documento produzido em parceria ou por autor vinculado à Fiocruz, mas não consta à informação no documento”.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), Fundação de Amparo a Pesquisa de Minas Gerais (FAPEMIG), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES).Mammary neoplasms are the third most frequent tumor in felines. We describe clinical, histopathological, and immuno-histochemical findings from a malignant adenomyo-epithelioma (MA) from a domestic queen. The cat presented with mammary masses and underwent radical unilateral mastectomy followed by chemotherapy. The tumor recurred and the animal survived 125 days but then died. Microscopy revealed a highly cellular malignant myoepithelial solid cell proliferation pattern with moderate pleomorphism and malignant epithelial proliferation in a tubular and papillary arrangement. The myoepithelial nature of the neoplastic cells was confirmed by p63 target antigen clone test. Based on histopathological and immunohistochemical findings and histological similarity between women and feline tumors, a diagnosis of MA was made.