DNA methylation is a well-defined epigenetic mechanism for the repression of gene expression22 and BRCA1 mutation is associated with specific global DNA methylation profiles in breast cancer.23 These findings suggested that BRCA1 deficiency may lead to DNA methylation and therefore the silencing of FOXA1. To test this conjecture, we studied the extent of DNA methylation in the CpG islands located within the Foxa1 gene promoter in the Brca1-deficient mouse epithelial cells (Figure 3c). Here, FOXA1 is linked to breast cancer.