Metaplastic Breast Cancer: Molecular Typing and Identification of Potential Targeted Therapies at a Single Institution.

Metaplastic breast carcinoma (MBC) is a rare and aggressive histologic subtype of breast cancer comprising approximately 0.5% to 5.0% of all invasive breast cancers with a poor prognosis and limited therapeutic options.,We investigated MBC at our institution to evaluate outcomes and investigate the molecular profile of our cohort to determine the presence of mutations for which there are targeted therapies.,We found our cohort to consist mainly of the matrix-producing variant (72%) with 48% having the stereotypical estrogen receptor-negative/progesterone receptor-negative/human epidermal growth factor receptor-2-negative phenotype. While the overall survival of our cohort was an average of 1679 days (4.6 years), we had a surprising number of patients with second primaries (40%) and distant metastases (40%), yet few recurrences (12%). Molecular analysis of the tumors indicated that one gene mutation, CSFIR, was significantly associated with outcome (P = .021); however, the cohort was defined by frequent mutations in ERBB4 (36%), PIK3CA (48%), and FLT3 (60%), for which there are now targeted therapies.,While surgery is the appropriate first step in the management of this aggressive malignancy, the collection of data pertaining to the use of targeted agents, although anecdotal, may provide clues to better treatment for these patients.