ESR1 and breast cancer: In Colombia, luminal B is the most prevalent (37.2%-50%) and triple-negative breast cancer the second (21%).33,39,40 BC subtypes are key prognosis determinants and predict treatment response.41 The standard of care is IHC for estrogen receptor, progesterone receptor, Ki 67, and HER2.33,39-41 NGS use and gene profiling in BC focused on identifying HBOC and specific early BC subtypes (ie, claudin-low androgen receptor, enriched mesenchymal-like, basal-like luminal HER2-enriched).