ES-HPBC can be broadly divided into luminal A [estrogen receptor (ER)/progesterone receptor (PR) strong positive, human epidermal growth factor receptor 2 (HER2) negative, well differentiated and less proliferative] and luminal B (ER/PR low to moderate positive, poorly differentiated and highly proliferative) subtypes with a 10-year breast cancer-specific overall survival (DSOS) of 92% (95% CI 90-94) and 79% (95% CI 74-85) respectively (p < 0.001) [1]. Here, ESR1 is linked to breast cancer.