GSTP1 and breast cancer: previous reports of DNA methylation in breast tumours or at least breast cancer cell lines (ABCB1 [11], ATM [12], BRCA1 [13], CDH3 [14], CDKN2A [13], ESR1 [15], GSTP1 [16], IGF2 [17], HMLH1 [13], PPP2R2B [18], PTEN [19]) or other cancers (CXCR4 [20]), 2.