ESR1 and breast carcinoma: On the basis of the distribution of intrinsic breast cancer subtypes, the HER2-enriched subtype comprises approximately 75% of HER2-positive/ER-negative and 30% of HER2-positive/ER-positive tumors and exhibits the characteristic HER2/EGFR pathway activation, high proliferation rate, and immune-activated stroma with elevated TIL levels.