130P Progesterone receptor (P) status and survival outcomes of ER-negative breast cancer: A population-based cohort study

PR status, one of the hormone receptors (HR), is a biomarker for breast cancer classification. However, the clinical outcomes and endocrine therapy response of isolated PR-positive (ER-PR+) patients are unclear. This study evaluates the prognostic role of PR status in ER-negative (ER-) breast cancer. Early-stage ER- invasive ductal carcinoma (IDC) patients from the Surveillance, Epidemiology, and End Results (SEER) database were studied. We used propensity score matching (PSM) to match patients with different PR statuses and evaluate their BCSS using the Kaplan-Meier method. PR+ patients were stratified by chemotherapy and matched, to investigate the impact of chemotherapy on their BCSS. Using the SEER database, we identified 32613 ER-Her-2- and 12230 ER-Her-2+ early-stage breast cancer patients diagnosed from 2010 to 2015. 1973 pairs of Her-2- patients and 764 pairs of Her-2+ patients were matched by propensity score. PR status did not affect the 10-year BCSS of either Her-2- (80.74% vs. 80.49%, P=0.918, HR 1.008, 95%CI 0.874-1.161) or Her-2+ patients (85.47% vs. 87.43%, P=0.212, HR 0.840, 95%CI 0.640-1.104). Among all 2737 PR+ patients, we stratified them by chemotherapy and performed propensity score matching, with 653 pairs finally included in the analysis. Chemotherapy improved the 10-year BCSS of all PR+ patients (86.68% vs. 79.02%, P1cm (T1cN0) (92.93% vs. 84.30%, P=0.008, HR 0.405, 95%CI 0.209-0.786), but not those with tumor ≤1cm (T1a+bN0) (95.45% vs. 94.56%, P=0.681, HR 0.801, 95%CI 0.278-2.310). PR status did not affect survival in either Her-2 group. However, chemotherapy improved survival for ER-PR+ patients, especially those with lymph node involvement or tumor size > 1 cm. This finding agreed with the current treatment for triple-negative and Her-2 amplified subtypes, showing PR status had little prognostic value in ER- patients. Our results implied PR+ patients might not benefit much from endocrine therapy, needing further confirmation by prospective trials.