Gallen consensus panel [16, 17] included this consideration as the basis for their clinical recommendations evolving from the classic 3-pathological biomarker approach (ER, PR, and HER2), which divided BC into luminal, HER2, and triple-negative subtypes [18], into a four-category classification that considered the Ki67 index as the fourth potential biomarker and aimed to subdivide luminal tumors into luminal A and B. Cheang and Prat classifications [5, 6] guided the definitions from the panel. This evidence concerns the gene ESR1 and breast cancer.