It is noteworthy that none of the ER+ cancers that retained wt BRCA1 expressed CK5/6 or 14, while the only ER+ cancers expressing these basal cytokeratins had lost wt BRCA1. However, as the majority of the ER+ cancers with loss of wt BRCA1 did not express either basal cytokeratin, this difference was not significant. This evidence concerns the gene ESR1 and cancer.