ESR1 and breast cancer: A 21-gene assay expression profile (OncoTypeDx) can identify patients unlikely to benefit from adjuvant cytotoxic chemotherapy in stage I, invasive, luminal type BC (estrogen receptor–positive/progesterone receptor–positive/HER2-negative).57 The TAILORx phase III trial proved that chemotherapy can be safely avoided in low- and intermediate-risk patients.