562 Background: The sensitivity of the estrogen receptor (ERα) to anti-estrogen therapy can be affected by phosphorylation events. In premenopausal breast cancer patients, phosphorylation of the ERα at serine 118 (ERαS118-p) is predictive for benefit from adjuvant tamoxifen. Since ERαS118-p represents the common hallmark of different signaling cascades that differ in E2 dependency, the resulting effect on estrogen sensitivity may differ between pre- and postmenopausal patients. Phosphorylation of serine 167 (ERαS167-p) has been associated with favorable disease outcome, but whether ERαS167-p can predict tamoxifen sensitivity is currently unknown. We tested the predictive value of both ERαS118-p and ERαS167-p for benefit from adjuvant tamoxifen in postmenopausal breast cancer patients. Methods: We collected primary tumor blocks from 563 ERα positive (stage I-III) postmenopausal patients who had been randomized between tamoxifen (1 to 3 years) vs. no adjuvant therapy (IKA trial). The median follow-up of patients without a recurrence event was 9.4 years. Immunohistochemistry was performed on a TMA using monoclonal antibodies for ERαS118-p and ERαS167-p. The percentage of positive nuclei was scored and a score of ≥ 10 % was considered as positive. Multivariate Cox models were used to assess hazard ratios (HRs) for recurrence free interval and the interaction between these phosphorylations and tamoxifen treatment. Results: We did not find a significant interaction between either ERαS118-p (p=0.99) or ERαS167-p (p=0.44) and tamoxifen, suggesting that the relative benefit from adjuvant tamoxifen in postmenopausal patients is not dependent on the presence of one of these phosphorylations. Both tamoxifen treated patients as well as control patients had a better prognosis when their tumor was positive for ERαS118-p (adjusted HR 0.60 p=0.02) or ERαS167-p (adjusted HR 0.62, p=0.02) compared to patients whose tumor did not express these ERα phosphorylations. Conclusions: In postmenopausal patients ERαS118-p and ERαS167-p are both associated with better prognosis, but do not predict differential benefit from tamoxifen.
Low Z‐4OHtam concentrations are associated with adverse clinical outcome among early stage premenopausal breast cancer patients treated with adjuvant tamoxifen
