ESR1 and breast carcinoma: With a deep understanding of the molecular mechanism of breast cancer, the diagnosis and treatment of breast cancer entered the era of molecular typing and precision treatment, and the breast cancer was sub-grouped into luminal A, luminal B, HER-2, and triple-negative breast cancers (TNBC) based on the expression of ER, PR, HER-2, and the Ki-67 proliferation index.