FoundationOne CDx is a U.S. Food and Drug Administration (FDA) approved companion diagnostic for the identification of patients with certain molecular subtypes of NSCLC (EGFR mutation, ALK rearrangement, or BRAF mutation), melanoma (BRAF mutation), colorectal cancer (KRAS or NRAS mutation), ovarian cancer (BRCA1 or BRCA2 mutation), or breast cancer (HER2 amplification) who might benefit from targeted therapy. The gene discussed is ERBB2; the disease is breast cancer.