ESR1 and breast cancer: Gallen consensusstatement classifies BC subtypes by immunohistochemistry findings for estrogen receptor (ER),progesterone receptor (PR) (together, the hormone receptors [HR]), HER2, and Ki67expression,18,19 into five major subtypes—luminal A(HR+/HER2–/Ki67Low), luminal B (HER2–)(HR+/HER2–/Ki67High), luminal B (HER2+)(HR+/HER2+), HER2-overexpressing (HR–/HER2+), andtriple negative (ER–/PR–/HER2–)—which we used in thisstudy.