Promoter Methylation and Genetic Polymorphism of GSTP1 in Thai Breast Cancers

Breast cancer is the most common malignancy of women. In Thailand, the incidence is 20.9/100,000 population. Among Thai women, the incidence of breast cancer is now higher than cervical cancer (Khuhaprema et al., 2010). Many genetic alterations are involved in the development of breast cancer, such as mutation, deletion, gene polymorphism and CpG-island hypermethylation, leading to gene inactivation and affecting protein function. Glutathione S-transferase P1 (GSTP1) is in a superfamily of enzymes involved in the detoxification of reactive carcinogen metabolites. GSTP1 is an important anti-carcinogenic protein (Ramos-Gomez et al., 2001). A single nucleotide polymorphism at codon 105 (A to G) in exon5 of the GSTP1 gene causes the substitution of isoleucine with valine (Allan et al., 2001); the valine allele may affect the enzyme function and be associated with susceptibility to breast (Kim et al., 2004) and prostate cancers (Cairns et al., 2001). The hypermethylation of the CpG islands located in the promoter region of genes may result in decrease gene expression, including GSTP1 (Lin et al., 2001). GSTP1