Estrogen Receptor α–Negative Breast Cancer Tissues Express Significant Levels of Estrogen-Independent Transcription Factors, ERβ1 and ERβ5: Potential Molecular Targets for Chemoprevention

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Abstract
We have investigated the expression of two estrogen receptor β (ERβ) isoforms, ERβ1 and ERβ5, which activate gene transcription independent of estrogen or growth factors, in ERα-negative breast cancer tissues. We report here, for the first time, that ERα-negative tissues express significant levels of ERβ1 and ERβ5, and their expression levels are not different from levels in ERα positive tumors. However, significant differences exist between the two racial groups, African American and Caucasian, in that the patients from the former group express higher levels of ERβ1 and ERβ5 but not ERα. These two transcription factors could be potential molecular targets for designing chemopreventive drugs to treat ERα-negative breast cancers.