Abstract P5-03-03: DNA Methylation of the Estrogen Receptor (alpha) Promoter Is Higher in Triple Negative Breast Cancers Compared to the ER Negative Sub-Type

Background: The incidence of Estrogen Receptor alpha (ER) negative breast cancer and triple negative cases in India is twice that of Western Caucasians. The underlying causes for this two fold difference are unclear. DNA methylation of the ER promoter is one of the mechanisms of gene silencing. Recent data from the West indicate that the ER promoter is weakly methylated in a majority of patients independent of ER status. Data from an Indian cohort found 66% of ER negative breast tumors to be methylated at the ER gene. However, the technique used, Methylation specific PCR (MSP) suffers from a number of disadvantages such as false priming and low specificity. We have checked the methylation status of ER promoter A by a quantitative method and correlated it with clinicopathological parameters such as ER, progesterone receptor (PR) and Her2 protein status. Materials and Methods: Tumor sections from 51 cases of primary invasive carcinomas were used for DNA extraction and bisulphite conversion. We adopted a quantitative method, Methylight assay for estimating the methylation status of the ER gene. Percentage Methylation Ratio (PMR) was computed and graded according to previously published standards. Methylation specific PCR was done for all these samples for comparison. Grade and Lymph node (LN) status were assessed. Immunohistochemistry was done to examine the status of ER, PR and Her2 protein. Results: 16.6% of the ER negative tumors were moderately methylated (PMR score 5-50) at the ER promoter while none of the ER positive tumors were methylated to the same extent. Among the Triple Negative (TN) tumors in our cohort, 25% were moderately methylated. MSP tends to overestimate the methylated tumors and indicated that 43.5% of the ER negative tumors and19.2% of ER positive tumors were methylated. Discussion: A subgroup of ER negative and triple negative Indian patients have enhanced methylation of the ER gene. However this does not account for the doubling of ER negative incidence. Our demographics of a large pre-menopausal population might explain some part of this increase. Methylation of ER promoter was highest in TN tumors. This finding hints towards epigenetic dysregulation being a trait of TN tumors. The possibility of reversing the ER status from negative to positive in the clinic has raised an interest in the mechanism by which ER is lost. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P5-03-03.