460 Differential Expression of Oestrogen Receptor Alpha, KI-67 and BCL-2 in Endometrial Polyps From Women Treated With Anastrozole and Tamoxifen

Background: The ‘Arimidex’, Tamoxifen, Alone or in Combination (ATAC) trial is a randomised double-blind trial to assess the efficacy of anastrozole alone, tamoxifen alone or in combination as adjuvant therapy for early breast cancer. The endometrial sub-protocol was designed to examine the effect of these treatments on the endometrium. Methods: Endometrial polyps were present in a number of women at baseline and after 1 year of treatment. The expression of oestrogen receptor alpha (ER), progesterone receptor (PgR), Ki-67 and Bcl-2 were compared in 23 polyps from postmenopausal women at baseline and after 1 year of treatment. Results: Differences in antigen expression occurred only in the stromal compartment not in the glands. There were no differences in expression of PgR in all polyp groups. All drug treatments decreased ER expression in the stroma (p < 0.015). Women treated with tamoxifen alone and in combination showed an increased stromal Ki-67 expression (p = 0.002 and p = 0.0015, respectively). Ki-67 expression in polyps from women treated with anastrozole was not significantly different to polyps at baseline, but was significantly different to those treated with tamoxifen (p = 0.007). Bcl-2 expression was lower in polyps from women treated with tamoxifen compared with polyps at baseline (p = 0.01). Conclusions: Anastrozole treatment reduces ER expression within the polyps but has no effect on proliferation or apoptotic markers. However, tamoxifen treatment alters ER expression, has a negative impact on apoptosis and induces proliferation within endometrial polyps.