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Abstract P2-14-07: Association between initiation of adjuvant chemotherapy beyond 30 days following surgery and overall survival among patients with triple-negative breast cancer

Background: The optimal time between surgery and initiation of adjuvant chemotherapy is unknown, though delayed time to chemotherapy (TTC) is associated with decreased outcomes of breast cancer patients. Recently, studies have suggested that the association might be subtype-dependent and that TTC within 30 days should be warranted particularly in high-risk triple-negative breast cancer (TNBC) patients. Objective: To determine the extent to which TTC beyond 30 days is associated with reduced overall survival (OS) in TNBC patients. Methods: Using the population-based nationwide Netherlands Cancer Registry we identified TNBC patients diagnosed between 2006 and 2014 who received adjuvant chemotherapy. We distinguished between patients who underwent breast-conserving surgery (BCS) versus mastectomy given the difference in preoperative characteristics and outcomes. Median (95% confidence interval) follow-up was 82.9 (80.5-86.5) and 81.4 (79.5-83.9) months, respectively. Main outcomes and measures: The association between TTC beyond 30 days and OS was estimated with hazard ratios (HR) using propensity-score matched Cox proportional hazard analyses separately for patients who underwent BCS and mastectomy. Results: In total, 3016 patients were included, of whom 1079 (35.8%) underwent BCS and 1937 (64.2%) underwent a mastectomy. In matched patients who underwent BCS, 10-year OS was significantly better for patients with TTC within 30 days compared to patients with TTC beyond 30 days (84.4% vs. 76.9%, P=0.001). Patients with TTC beyond 30 days were more likely than those with TTC within 30 days to die within 10 years after surgery (HR 1.69 (95% CI 1.22-2.34), P=0.002). In matched patients who underwent mastectomy, there was no difference in 10-year OS between those with TTC within or beyond 30 days (74.5% vs. 74.7%, P=0.716), nor an increased risk of death for those with TTC beyond 30 days (HR 1.04 (95%-CI 0.84-1.28), P=0.716). In both populations, the associations were independent of adjuvant radiotherapy. Conclusions: The current results suggest that initiation of chemotherapy beyond 30 days is associated with decreased OS in TNBC patients who underwent BCS; no association was observed for patients who underwent a mastectomy. Therefore, timelier initiation of chemotherapy in TNBC patients undergoing BCS seems warranted. Citation Format: Erik Heeg, Perla J. Marang-van de Mheen, Marissa C. Van Maaren, Kay Schreuder, Rob A.E.M. Tollenaar, Sabine Siesling, Monique E.M.M. Bos, Marie-Jeanne T.F.D. Vrancken Peeters. Association between initiation of adjuvant chemotherapy beyond 30 days following surgery and overall survival among patients with triple-negative breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-14-07.