Background: The majority of breast cancers are hormone receptor positive, defined as estrogen receptor (ERα) and/or progesterone receptor (PR) positive. Adjuvant tamoxifen decreases the risk of recurrence and improves survival in hormone positive breast cancer, irrespective of age. Still some do not respond to tamoxifen. The clinical significance of ERα is still unclear, even if studies indicate that ERα might be of importance. The aim of this study was to investigate the tumor expression of ERα in premenopausal women with breast cancer and the relationship to other clinical and pathological parameters and if there is any prognostic or predictive value. This is the first study of ERα based on a randomized study including only premenopausal women.

Material and Methods: Premenopausal women (n=564) with breast cancer, Stage II (UICC), were randomized to either two years of adjuvant tamoxifen (n=276) or no tamoxifen (n=288). The median follow-up was 13.9 years. The expression of ERα (n=303) and ERα (n=309) was analyzed by immunohistochemistry (IHC) using tissue microarrays (TMA). ERα was considered positive if more than 50% of the cells were stained (n=174). ERα was scored according to number of positive cells and the intensity of the staining. ERα negative (n=70) score 0, 1-49% (n=137) score 1, 50-100% (n=102) score 2 and the intensity negative (n=70) score 0, weak (n=119) score 1, strong (n=120) score 2. ERα summary score 4 was considered positive (n=118).

Results: ERα was correlated with lymph node status (p=0.024), ERα (p=0.00016), PR (p=0.0084), Ki67 (p=0.035), cyclin D1 (P>0.00001) but showed a negative correlation to HER2 (p=0.042). Patients with ERα+/ERα- tumors showed significant benefit from 2 years of tamoxifen compared to those with ERα-/ERα — tumors (table1). In the control group ERα showed no prognostic value.

Recurrence free survival (RFS) at 10 years tamoxifen vs control

Discussion: ERα might be a tamoxifen predictive factor in ERα negative premenopausal breast cancer. If so, further studies are motivated to explore whether a subset of patients with triple negative breast cancer could benefit from endocrine therapy.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr PD05-06.