GSTP1 and cancer: We chose 19 well-characterized cancer-related genes such as tumour protein p53 (TP53), phosphatase and tensin homologue (PTEN) and oestrogen receptor 1 (ESR1), as well as 4 genes frequently differentially methylated in cancer, such as APC-WNT signaling pathway regulator adenomatous polyposis coli (APC), RAS association domain family member 1 (RASSF1), glutathione S-transferase pi 1 (GSTP1) and O-6-methylguanine-DNA methyltransferase (MGMT)(see Methods).