24 Background: Estrogen receptor (ER)-positive breast cancers are considered prognostically more favorable than ER-negative tumors and are often responsive to anti-estrogen therapy. Whereas tumors overexpressing HER2 are endocrine resistant and they require the blockage of the HER2 pathway in addition to estrogen deprivation. To evaluate epigenetics differences in tumor-related genes to ESR1 and HER2/neu status in primary breast cancer is the objective of this study. Methods: We quantified methylation levels of promoter of ERS1 which are to confer growth adventage to cells in 107 women with breast cancer. Real Time QMS-PCR SYBR green (methylation-specific PCR) was used to analyze the hypermethylation. Tumours were classified as phenotype basal, luminal A, Luminal B, and phenotype HER2+. Results: Presence of methylated ESR1 in serum of breast cancer patients was associated with ER-negative phenotype (p=0.0179). Of the available cases, 60 pts (56%) were Luminal A, 10 pts (9.3%) Luminal B, 13 pts (12%) Basal like, and 9 pts (8.4%) HER2+. We observed that methylated ERS1 was preferably associated with phenotype Basal Like and worse interval progression free and survival global though p > 0.05 and the amplification HER2+ was correlation with significant more frequent methylation gene (p<0.05). Thet hypermethylation of normal ERS1 and 14-3-3σ combined differentiated between breast cancer patients and healthy controls (p = 0.0001) with a sensitivity of 81% (95% CI: 72–88%) and specificity of 88% (95% CI: 78–94%). Conclusions: This study identifies the presence of variations in global levels of methylation promoters genes in healthy controls and breast cancer with different phenotype classes and shows that these differences have clinical significance. These showed that frequent methylation had a strong association with molecular phenotype of breast cancer and perhaps in the future can explain therapy resistance related to RE and HER2/neu status and this may be of significance in the assessment of targeted therapy resistance related to ER and HER2/neu status in breast cancer patients.