Abstract P4-08-01: Is the 8th edition of the breast cancer TNM staging system an improvement over the 7th edition?

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Abstract Background: The revised 8th edition of the TNM staging system was published on January 25, 2018 (https://cancerstaging.org/references-tools/deskreferences/Pages/Breast-Cancer-Staging.aspx). The new prognostic staging system (PrSS) was developed using the outcomes of 334,243 patients from the National Cancer Database (NCDB) with a median follow-up of 3.5 years after treatment in 2010-2012. The PrSS was created by clustering patients by outcome into the eight sub-stages of the 7th edition TNM anatomic staging system (AnSS) using more than 169 combinations of stage, ER, PR, H2, grade and molecular test results. This study aimed to assess the prognostic performance of the PrSS in an independent cohort with longer follow-up. Methods: The Breast Cancer Unit Outcomes database was used to identify patients treated without neoadjuvant systemic therapy in 2005-2014, when use of anti-Her2 therapies was routine. Ten-year breast cancer-specific survival (BCSS) was determined using the Kaplan-Meier method. Using age, ER, PR, H2, grade, chemotherapy, type of surgery and radiotherapy variables for the AnSS and the same variables minus ER, PR, H2, and grade, which are built into the PrSS, Harrell's c-indices were calculated to compare the predictive performance of the AnSS and PrSS models (higher quality models have higher c-indices). Results: The study cohort had 19,581 patients with a median follow-up of 7.3 years. Relative to the AnSS, 5.2% (1009/19,581) had higher prognostic stages and 36.5% (7,149/19,581) had lower prognostic stages. The c-indices were 0.83 for the AnSS and 0.81 for the PrSS. Overlapping 10-year BCSS confidence intervals (CI) were observed for stages IIIB and IIIC, which contained few patients in both staging systems. There were also overlapping CIs for two other anatomic stages: IA & IB and four other prognostic stages: IB & IIA and IIB & IIIA. Comparison of Anatomic and Prognostic TNM Staging Number of Patients10-year BCSSStagesAnatomicPrognosticAnatomic (%) (CI)Prognostic (%) (CI)IA9,19511,98796.4 (95.8, 96.9)95.9 (95.4, 96.4)IB6083,01595.1 (92.2, 96.9)86.7 (84.9, 88.3)IIA4,8402,03889.9 (88.7, 91.0)85.4 (83.4, 87.1)IIB2,49586983.9 (81.9, 85.7)73.9 (70.0, 77.4)IIIA1,54978975.0 (72.0, 77.6)70.8 (66.7, 74.5)IIIB9435754.8 (40.3, 67.2)57.1 (50.4, 63.2)IIIC53926553.0 (47.6, 58.1)50.8 (43.7, 57.4)IV26126123.8 (17.6, 30.5)23.8 (17.6, 30.5) Conclusions: For 10-year BCSS, the c-index was higher for the AnSS than for the PrSS. In addition, more statistically distinct stages were observed for the AnSS than the PrSS. The increased complexity of the PrSS did not appear to provide better prognostication than the AnSS in our large series with longer follow-up than the NCDB. Citation Format: Nichol AM, Lohrisch CA, Gondara L, Speers CH, Gelmon KA. Is the 8th edition of the breast cancer TNM staging system an improvement over the 7th edition? [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-08-01.