Background: The initiation and progression of breast carcinoma are profoundly influenced by hormonal factors. Breast tumors that express the estrogen receptor (ER) are slower growing, associated with better long-term disease-free survival, and amenable to endocrine therapy with agents such as the antiestrogen. But only 60% of the ER-positive breast cancer patients respond to endocrine manipulation. In addition, many ER-positive cancers that initially respond to endocrine therapy ultimately progress to a more aggressive hormone-independent phenotype. Loss of estrogen receptor expression is an important means of hormone resistance, but the mechanisms involved are poorly understood. Materials & Method: We examined the ER by dextran-coated charcoal assay and the ER cDNA by reverse transcription-palymerase chain reaction in 19 primary breast cancers to determine if alterations of the gene are associated with the ER-negative status. Results: From this study, we could see the expression of the ER gene in all of the ER- positive specimens, but ER-negative group showed inconsistent results. Four out of 9 ER- negative specimens expressed ER gene. Three of these four were progesterone receptor-positive. Conclusion: This results suggest that ER expression may be determined at the transcription level and that genomic analysis of the ER may be more accurate than conventional ER assays in clinical setting.
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