Association of estrogen receptors' promoter methylation and clinicopathological characteristics in Iranian patients with breast cancer
Molecular and Biochemical diagnosis (MBD)
Estrogens play a substantial role in the proliferation, progression and treatment of breast cancer by binding with two estrogen receptors, alpha and beta (ER and ER). Resistance to endocrine therapy is a major problem in the treatment of breast cancers and, in some cases, may be related to loss of ER gene expression. We have already showed that ER methylation occurs in high frequency and may be one of the important mechanisms for ER gene silencing in a subset of Iranian primary sporadic breast
... ry sporadic breast cancers. In the other hand, the CpG Island methylation status of ER and the relationship between clinicopathological features and the pattern of ER methylation in sporadic breast cancer are still unknown, especially in Iranian women. Methods: In this study, we examined the exact role of DNA methylation in the estrogen receptors, alpha and beta genes using Combined Bisulfite Restriction enzyme Analysis (COBRA) and Methylation specific polymerase chain reaction (MSP) methods in 34 tissue and 40 peripheral white blood cells in the breast cancers. Results and Conclusions: ER promoter methylation was identified in 29(72.5%) tissue samples and 35(87.5%) peripheral blood. Among these ER-methylated cases, the co-occurrent methylation of ER promoter in peripheral blood and tissue samples was evident in 25 (71.4%) patient (P=0.56). Furthermore, ER promoter methylation was detected in 13(32.5%) tissue samples and 4(10.0%) peripheral blood specimens. Of these ER-methylated cases, the co-ocurrent methylation of ER promoter in the peripheral blood and tissue samples was evident in 1(7.7%) patient (P= 0.11). Based on COBRA analysis the percentage of DNA methylation at methylation-sensitive BstUI restriction site of the ER promoter A ranged from 1% to 91%. The percentages at promoters A region showed a borderline associations with lymph node involvement (P=0.079, r=0.55) and a significant correlation with the grade of tumors (p= 0.27, r=0.65). No significant relation was found between ER promoter and ER promoter methylation (Odds ratio =2.82, 95%, CI =0.28-28.5, P=0.36). The methylation of promoter ON was observed in only a subset of tumors without ER by IHC. In addition, we did not find any significant correlation between the prognostic factors such as grade, tumor size, lymph node involvement, and methylation status of this promoter. Our results indicate that methylation of ER promoter ON is not responsible for the loss of gene expression in of all breast tumors.