Abstract
574 Background: ERα is the main prognostic and therapeutic marker in breast cancer (BC). About 30% of BC cases are negative for ER (ERα-) and do not benefit from antiestrogen therapy (TAM). We aim to study ER-beta (ERβ) expression in ERα- and triple negative (TN) cancers to explore alternate pathway of treatment in this cohort. Methods: We studied 67 ERα- BC cases including 44 TN together with 74 ERα +BC cases obtained from patients aged 29 to 97 years old between 2003 and 2010. The histology included 110 intraductal, 12 medullary and 19 other types. 78 cases were grade 3, 52 were grade 2, and 11 were grade 1. RNA was extracted from FFPE and mRNA levels of ERβ isoform and ERα were determined by real-time quantitative reverse transcription PCR. IHC stains were done on TMA the sections for ERα, PR, Her-2, Ki-67, CK5/6 and Cyclin D1. Results: ERβ isoforms were highly expressed in ERα-, TN, basal-like and HER2 type BC cases. ERβ2 was the major ERβ variant expressed. Ki-67 proliferating cells (>20% nuclear staining) were mostly in ERα- rather than ERα+ cases (69.0% vs. 31.0%) as were cyclin D1- cells (82.2% vs. 17.8%). On the other hand, in ERα+ BC, ERα mRNA expression was consistently high and upregulated, and ERβ, low and down regulated, and the ratio of ERα+ to ERβ+ ranged from 3 to 100. ERβ1, 2 and 5 were co-expressed with ERα in 56%, 63%, and 30% of cases, respectively. Overall, ERβ mRNA levels did not show any significant correlation with age, tumor size, lymph node status and histological grades. Conclusions: ERβ-dependent proliferating tumor cells may render them more sensitive to TAM, and increase the effectiveness of TAM and its metabolites in ERα- and TN cases. Increased overall survival after adjuvant TAM ERα-BC may be directly related to ERβ over-expression. ERβ isoform is potential selective therapeutic target in a sub-cohort of ERα- BC. Additionally, when ERβ and ERα are co-expressed, ERβ appears to play a distinct role from its action in ERα- BC. [Table: see text]
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