ESR1 and breast cancer: For example, breast cancer in females with epidermal growth factor receptor 2 (EGFR‐2, or HER‐2), positive with or without HR‐positive or triple‐negative subtypes (estrogen receptor (ER) negative, progesterone receptor (P.R.)negative, and normal HER2 levels) is associated with an increased odds ratio for developing BMs than those with ERpositive and/or PRpositive breast cancer.43