A New Landscape of Testing and Therapeutics in Metastatic Breast Cancer.

Predictive biomarker testing on metastatic breast cancer is essential for determining patient eligibility for targeted therapeutics. The National Comprehensive Cancer Network currently recommends assessment of specific biomarkers on metastatic tumor subtypes, including hormone receptors, HER2, and BRCA1/2 mutations, on all newly metastatic breast cancers subtypes; programmed death-ligand 1 on metastatic triple-negative carcinomas; and PIK3CA mutation status on estrogen receptor-positive carcinomas. In select circumstances mismatch repair protein deficiency and/or microsatellite insufficiency, tumor mutation burden, and NTRK translocation status are also testing options. Novel biomarker testing, such as detecting PIK3CA mutations in circulating tumor DNA, is expanding in this rapidly evolving arena.