Oestrogen receptor-a (ERa) is an important prognostic marker in breast cancer and endocrine therapies are designed to inhibit or prevent ERa activity. In vitro studies have indicated that phosphorylation of ERa, in particular on serine 118 (S118), can result in activation in a ligandindependent manner, thereby potentially contributing to resistance to endocrine agents, such as tamoxifen and aromatase inhibitors. Here we report the immunohistochemistry (IHC) of S118 phosphorylation in 301 primary breast tumour biopsies. Surprisingly, this analysis shows that S118 phosphorylation is higher in more differentiated tumours, suggesting that phosphorylation at this site is associated with a good prognosis in patients not previously treated with endocrine agents. However, we also report that S118 phosphorylation was elevated in tumour biopsies taken from patients who had relapsed following tamoxifen treatment, when compared to pre-treatment biopsies. Taken together, these data are consistent with the view that S118 phosphorylation is a feature of normal ERa function and that increases in levels of phosphorylation at this site may play a key role in the emergence of endocrine resistance in breast cancer.

197 Background: DNA methytransferase inhibitors and histone deacetylase inhibitors have been extensively studied in recent years as another novel and specific target therapy for cancer treatment. In this study, we investigate the effect of combined therapy of 5-aza-2’-deoxycytidine (5-aza-CdR), sodium butyrate (SB) and tamoxifen on tumor suppression and expression of anti- or proapoptic proteins in breast cancer cell lines. Methods: Water-soluble tetrazolium salt-1 was used to study the proliferation rate of the cells in MDA-MB-231 and MCF-7 breast cell lines treated with the different concentration of variable combinations of these agents. Western blot was used to explore the change of expression of proapaptic regulator proteins according to variable combined therapy. Methylation specific transcriptase-polymerase chain reaction and immunofluorescence staining were used to analyze the ER re-expression in the MDA-MB-231 and MCF-7 cell lines treated with 5-aza-CdR. Results: We observed that the survival fraction of MCF-7 and MDA-MB-231 cells treated with 2um, 4um, 8um 5-aza-CdR and 0.5mM, 1mM and 2mM SB respectively was decreased in inverse proportion to the concentration. The survival fraction of MCF-7 cells as ER positive cell lines treated with 2.5um, 5um and 10um tamoxifen was slightly decreased in inverse proportion to the concentration, but that of MDA-MB-231 cells as ER negative cell lines was slightly increased regardless the concentration. ER re-expression was detected in ER negative cell line, MDA-MB-231 treated with 5-aza-CdR. In cases of being treated with variable combination of agents in MCF-7 and MDA-MB-231 cell lines, the survival fraction treated with the combination of all 5-aza-CdR, SB and tamoxifen was the lowest. We also observed that the expression of proapoptic regulator protein were slightly decreased in MCF-7 and MDA-MB-231 cells treated with combined 5-aza-CdR with SB and combined with all agents. Conclusions: Our data indicate that combined therapy with 5-aza-CdR, SB and tamoxifen was the most effective in apoptosis of breast cancer cells and changed expression of the proapoptic regulator proteins.