A Clinical Analysis of Methylation Status of Tumor Suppressor Genes in Breast Cancer

ABSTRACT

PURPOSE: Aberrant methylation of CpG islands in gene promoters has been considered as a common mechanism for suppressing gene expression in cells. Hypermethylation of CpG islands in promoters is associated with silencing of transcription in various tumor suppressor genes and recent studies identified a CpG island methylator phenotype (CIMP) suggesting common methylation defect in cancer cells. For breast cancer, several genes were previously reported to be hypermethylated, but it is unclear whether the CIMP status is associated with any clinicopathological characteristics of breast cancer. In this study, we investigated the methylation patterns of several genes such as p16(INK4a), O(6)-methyguanine-DNA methyltransferase (MGMT), Death associated protein kinase (DAPK), E-cadherin, hMLH1, and four loci such as Methylation in tumor (MINT MINT1, MINT2, MINT25, MINT31) and analyzed the correlation with clinical features. METHODS: 85 patients who underwent curative surgery for breast cancer were studied retrospectively using their paraffin-embedded tissues and medical records. Immunohistochemical staining were performed according to their hormone receptors. DNA extraction, sodium bisulfite modification and methylation specific PCR (MSP-PCR) were performed with some modifications. RESULTS: The rates of E-cadherin and MINT 31 methylation in cancer tissue were significantly higher than those of normal tissues (P<0.05). There was no statistical correlation between methylation status of each suppressor genes and hormone receptor except DAPK methylation with progesteron receptor. The rate of E-cadherin methylation was significantly high in stage II (P=0.010). For 5-year survival and disease-free survival rate, the group with methylated MINT1 and MINT25 had significantly better outcome than unmethylated group (P<0.05). There was no statistical significance between CIMP status and other prognostic factors such as hormone receptor and stage (P=0.885). But, CIMP-High group was significantly lower than CIMP-Low group in 5-year survival (P=0.001) and disease-free survival rate (P=0.024). CONCLUSION: The methylation of E-cadherin and some MINT loci seems closely related to tumorigenesis in breast cancer and CIMP status have some value as a prognostic indicator after surgery in breast cancer but more large scale study will be needed.