By these analyses breast cancers are classified as luminal A (ER+ and/or PR+, Ki67 low and HER2−), luminal B HER2− (ER+ and/or PR+, Ki67 high and HER2−), luminal B HER2+ (ER+ and/or PR+, any Ki67 and HER2+), HER2-type (ER−, PR− and HER2+) and triple-negative (ER−, PR− and HER2−) [6]. The gene discussed is ESR1; the disease is breast cancer.