We focus on clinically relevant patient subgroups including all, ER-positive/lymph node negative/human epidermal growth factor receptor 2 negative (ER+/LN−/HER2−), ER+/LN+/HER2−, HER2+ and triple negative breast cancers (TNBCs), as well as the PAM50 subtypes (luminal A, luminal B, HER2-enriched and basal-like) and treatment-specific subgroups (patients who received chemotherapy, endocrine therapy, both sequentially or untreated). Here, ESR1 is linked to triple-negative breast carcinoma.