Mammary Epithelial-Myoepithelial Carcinoma: Report of a Case With HRAS and PIK3CA Mutations by Next-Generation Sequencing

We present the case of a 73-year-old woman with an epithelial-myoepithelial carcinoma of the left breast (ie, malignant adenomyoepithelioma). In both the initial needle core biopsy and in the subsequently performed lumpectomy, the tumor consisted of nests of neoplastic epithelium and myoepithelium with cytologic atypia, increased mitoses, and infiltrative growth into the surrounding tissue. Mutational analysis showed oncogenic driver mutations in HRAS and PIK3CA. In this article, we describe an epithelial-myoepithelial carcinoma of the breast with focal metaplastic differentiation, an extremely rare entity, and report the results of targeted next-generation sequencing. Our patient has not shown any evidence of recurrent or metastatic disease at 29 months follow-up.