To date, from a consecutive series of 197 breast cancers in which CK19 expression was assessed, we found lack of CK19 expression in 3.5 % (2/57) of breast cancers with a luminal A phenotype (ER/PR+, Her2−, Ki67 < 14 %), 2.9 % (3/103) of breast cancers with a luminal B phenotype (ER/PR + and Ki67 > 14 % or Her2+), and 4.2 % (1/24) in triple-negative carcinomas. Here, ESR1 is linked to breast cancer.