ESR1 and neoplasm: The multi‐gene expression‐based assay, Oncotype DX (ODX‐Genomic Health, Redwood City, CA), is a genomic tumor profiling tool that determines the expression of 21 tumor‐associated genes; it helps determine the risk for distant recurrence and whether chemotherapy is an appropriate course of treatment in patients with early stage, ER positive, HER2 negative, and lymph node negative (or 1–3 positive lymph nodes) invasive BCa.