Association of the phosphorylation of the estrogen receptor at serine 118 and 167 with prognosis in postmenopausal breast cancer patients.

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 pat...