There is evidence to suggest that DNA methylation is gradually lost passively through many rounds of cell division29 and during breast epithelial cell immortalization.32 In agreement, bisulphite-converted PCR analysis showed that the FOXA1 promoter region is hypomethylated in BRCA1-positive as well as negative human breast cancer cell lines (Supplementary Figure S4). Here, FOXA1 is linked to breast carcinoma.