Whilst the distribution of PALB2-associated breast cancers into ER/HER2 clinical subgroups was found to be comparable to that of sporadic and BRCA2 breast cancers,19,21 it differed from that of BRCA1 breast cancers, which are preferentially of triple-negative phenotype (approximately 70%–85%).21–23. This evidence concerns the gene ESR1 and breast cancer.