ESR1 and neoplasm: Conventional histopathological and molecular analyses have demonstrated familial BRCA1 tumours to have a basal-like phenotype and to be significantly associated with certain features, such as AI at the BRCA1 locus, a negative estrogen receptor (ER) and progesterone receptor (PR) status, a medullary tumour histological type, TP53 mutations and, depending on the mutation involved, a high tumour grade [3,5,18,20,21].