Malignant adenomyoepithelioma with HRAS G13R mutation: A case report

Adenomyoepithelioma (AME) of the breast is a rare tumor characterized by epithelial and myoepithelial differentiation, with a hotspot mutation in <i>HRAS</i> Q61. Malignant transformation occurs from either the luminal or myoepithelial component. In the present study, a malignant AME (M-AME) with pulmonary metastasis is reported. M-AME is rare, and the present report highlights the genomic alteration of primary and metastatic lesions. A 53-year-old Japanese woman presented to a neighboring clinic with a palpable and non-tender mass in the left breast. The mass was suspected to be AME, and left mastectomy was performed at Osaka Medical and Pharmaceutical University (Takatsuki, Japan). Breast tumor specimens exhibited epithelial and myoepithelial proliferation with myoepithelial mitoses and necrosis, and the tumor was diagnosed as M-AME. Following chemotherapy, a lung tumor was identified 2 years after the operation. The pulmonary tumor indicated myoepithelial cell proliferation along the bronchiolar epithelium, and myoepithelial cells exhibited clear or epithelioid features. Both the breast and lung tumor exhibited the <i>HRAS</i> G13R mutation, which is frequently observed in M-AME. This mutation may be considered a driver mutation in mammary M-AME.