Abstract P3-07-19: Progesterone receptor positivity is an independent predictor of long-term benefit from adjuvant tamoxifen treatment of estrogen receptor positive breast cancer

Introduction:The expression of estrogen receptor (ER) and progesterone receptor (PgR) predicts the response to endocrine therapy of breast cancer. Nearly all PgR positive tumors are also ER positive. The independent predictive information of PgR has been questioned after an overview by the EBCTCG. However, the studies in the overview were performed before modern PgR immunohistochemistry (IHC) was developed. Purpose: We aim to investigate the independent predictive value of PgR determined by IHC in ER positive tumors. Materials and methods: Between 1976 and 1990 the Stockholm Breast Cancer Study Group conducted a randomized trial comparing adjuvant tamoxifen versus control. We evaluated 618 patients with ER-positive "low-risk" breast cancer ( tumor size≤ 30 mm and lymph node-negative) for whom PgR was determined by immunohistochemistry. The median follow-up was 17 years. Hazard ratios (HRs) and 95 % confidence intervals (CIs) were estimated using the Cox9s proportional hazards model. Results: Patients with ER+/PgR+ tumors receiving tamoxifen had a reduced recurrence risk compared with those who were not treated with tamoxifen (HR= 0.40, 95% CI 0.27 – 0.59, p Conclusion: Our results indicate that the PgR expression adds predictive value to the ER expression regarding benefit from tamoxifen treatment. Citation Format: Fohlin H, Nordenskjold A, Fornander T, Lofdahl B, Skoog L, Stal O. Progesterone receptor positivity is an independent predictor of long-term benefit from adjuvant tamoxifen treatment of estrogen receptor positive breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-07-19.