Gallen International Breast Cancer Conferences 2011 and 2013, it was agreed that the different breast cancer intrinsic subtypes can be defined not only by genetic array testing but also by an approximation to this classification that can be made by immunohistochemistry, and a definition of intrinsic subtypes of breast cancer was suggested: luminal A (ER+ and/or PR+, Ki67 low and Her2−), luminal B (ER+ and/or PR+, Ki67 high and/or Her2+), Her2-positive (ER−, PR− and Her2+), and triple-negative (ER−, PR−, Her2−) [5,6,7]. The gene discussed is ESR1; the disease is breast cancer.