Context.-Metastatic metaplastic breast carcinoma (MPBC) is an uncommon, but aggressive, tumor resistant to conventional chemotherapy.Objective.-To learn whether next-generation sequencing could identify potential targets of therapy for patients with relapsed and metastatic MPBC.Design.-Hybridization capture of 3769 exons from 236 cancer-related genes and 47 introns of 19 genes commonly rearranged in cancer was applied to a minimum of 50 ng of DNA extracted from 20 MPBC formalin-fixed, paraffinembedded specimens and sequenced to high uniform coverage.Results.-The 20 patients with MPBC had a median age of 62 years (range, 42-86 years). There were 9 squamous (45%), 9 chondroid (45%), and 2 spindle cell (10%) MPBCs, all of which were high grade. Ninety-three genomic alterations were identified, (range, 1-11) with 19 of the 20 cases (95%) harboring an alteration that could potentially lead to a targeted treatment option. The mostcommon alterations were in TP53 (n ¼ 69; 75%), PIK3CA (n ¼ 37; 40%), MYC (n ¼ 28; 30%), MLL2 (n ¼ 28; 30%), PTEN (n ¼ 23; 25%), CDKN2A/B (n ¼ 19; 20%), CCND3 (n ¼ 14; 15%), CCNE1 (n ¼ 9; 10%), EGFR (n ¼ 9; 10%), and KDM6A (n ¼ 9; 10%); AKT3, CCND1, CCND2, CDK4, FBXW7, FGFR1, HRAS, NF1, PIK3R1, and SRC were each altered in a single case. All 16 MPBCs (100%) that were negative for ERBB2 (HER2) overexpression by immunohistochemistry and/or ERBB2 (HER2) amplification by fluorescence in situ hybridization were also uniformly (100%) negative for ERBB2 amplification by next-generation sequencing-based copy-number assessment.Conclusions.-Our results indicate that genomic profiling using next-generation sequencing can identify clinically meaningful alterations that have the potential to guide targeted treatment decisions in most patients with metastatic MPBC.