Introduction: The estrogen receptors are potential candidates in prognosis and particularly in predicting hormone response therapy in breast cancer. The aim of this study was to measure ERα gene expression due to study of the association between ERα expression, age and menopause of Iranian women with breast cancer. Methods: 21 adenocarcinoma cases with grade 2 and 10 normal samples were screened before treatment and without contamination. After RNA extraction and cDNA synthesis, ERα and GAPDH genes for measurement of relative quantification were amplified by Real-time PCR according to the standard method. Specificity of amplification products was confirmed by melting curve analysis. The obtained Ct and Ct values were analyzed by SDS v1.4 software, GLM program and student’s t tests procedure were performed in SAS v9.1 software to determine statistical significance Results: The results indicated that ERα gene in malignant cases was over expressed (P<0.01). The statically significant difference test between gene expressions in malignant cases in comparison with non-malignant samples showed that ERα gene expression increased in 100 percent of malignant cases. ERα expression showed narrow variations in tumor tissues too. Also the amount of ERα mRNA increased with age and was consequently higher in postmenopausal patients\' tumors (P<0.01). Conclusion: This study results indicated that ERα can be used as a biomarker for prognosis, screening and diagnosis of malignant patients against normal persons even, at the beginning stages of breast cancer. Furthermore, this method can be help to patient selection for anti-estrogen therapy and monitoring response to therapy.

Keywords