Abstract P5-06-19: AJCC 8th edition prognostic staging system provide no better discriminatory ability in prognosis than anatomical staging system in triple negative breast cancer: A cohort from two institutions and a large population based study

Background The American Joint Committee on Cancer (AJCC) eighth edition cancer staging manual has updated with a prognostic stage group for breast cancer by incorporating traditional TNM anatomic parameters and biomarkers (ER, PR, Her-2 status and tumor grade, etc.). In this study, we retrospectively compared the prognostic value between the AJCC 8th Edition anatomic and prognostic staging system for triple negative breast cancer(TNBC) in a cohort from two involved institutions and a large population database. Design Clinicopathological data of patients who underwent breast surgery as the initial intervention and with TNBC were identified in Sun Yat-sen University Cancer Center(SYSUCC) during 2005-2013 and Prince of Wales Hospital (PWH) during 2002-2008. Data from surveillance, epidemiology, and end results (SEER) database during 2010-2015 was also accessed. We restaged all cases into anatomic stage (AS) and prognostic stage (PS) group according to the AJCC 8th Edition staging system. The Kaplan-Meier analysis with log-rank test was used to compare differences in disease-specific survival (DSS), overall survival (OS) and progression-free survival (PFS) between groups. The Harrell concordance index (C index) was calculated to measure predictive performance for the AS and PS models. The relationshipof AS and PS with DSS, PFS or OS was examined using a Cox proportional hazards regression model. Results A total of 611 patients with stage I to IIIC TNBC were identified in the SYSUCC-PWH cohort with a median follow-up of 53.5 months. Compared with the AS, PS upstaged 46.1% of patients. No patient was downstaged by PS in this cohort. No significant difference was observed in C index between AS and PS models for either DSS (0.84 vs. 0.83, p=0.943) or PFS (0.82 vs. 0.80, p=0.887), demonstrating that PS do not reflect a more accurate predictive model than AS. A total of 31941 patients with stage I to IIIC TNBC were identified in the SEER cohort with a median follow-up of 27 months. PS upstaged 62.4% of patients and downstaged eight patients (from IIIC to IIIB) in this cohort. Similarly, PS model do not performed better than the AS in either DSS (C index, 0.85 vs. 0.86, p=0.95) or OS (C index, 0.90 vs. 0.90, p=0.98). Compared those with stage changed to other without, in SYSUCC-PWH cohort, patients with IIIC unchanged stage showed worse PFS compared to patients with AS IIIA or IIIB upstaged to PS IIIC (p=0.049). Similarly, in SEER cohort, patients with IIIC unchanged stage showed worse OS and DSS compared to patients with AS IIIA or IIIB upstaged to PS IIIC (p Citation Format: Peng Sun, JYS Tsang, Xiaodan Xu, Jibin Li, Mei Li, Xue Chao, Rongzhen Luo, Gary Tse, Jiehua He. AJCC 8th edition prognostic staging system provide no better discriminatory ability in prognosis than anatomical staging system in triple negative breast cancer: A cohort from two institutions and a large population based study [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 P5-06-19.