Validation of Prognostic Stage and Anatomic Stage in the American Joint Committee on Cancer 8th Edition for Inflammatory Breast Cancer

SIMPLE SUMMARY: This study is the first to confirm that the clinical prognostic stage in the American Joint Committee on Cancer (AJCC) 8th edition provides a more accurate prognostication for inflammatory breast cancer than the traditional anatomic stage. It indicated that incorporating biological factors into the traditional staging system provides more accurate inflammatory breast cancer (IBC) prognosis stratification than does the tumor size (T) and presence of lymph node involvement (N) and distant metastasis (M) (TNM) staging system. Our results show that the AJCC prognostic staging system is optimal for prognostication in IBC. ABSTRACT: The AJCC updated its breast cancer staging system to incorporate biological factors in the “prognostic stage”. We undertook this study to validate the prognostic and anatomic stages for inflammatory breast cancer (IBC). We established two cohorts of IBC diagnosed without distant metastasis: (1) patients treated at The University of Texas MD Anderson Cancer Center between 1991 and 2017 (MDA cohort) and (2) patients registered in the national Surveillance, Epidemiology, and End Results (SEER) database between 2010 and 2015 (SEER cohort). For prognostic staging, estrogen receptor (ER)+/progesterone receptor (PR)+/ human epidermal growth factor receptor-2 (HER2)+/grade 1–2 was staged as IIIA; ER+/PR−/HER2−/grade 3, ER−/PR+/HER2−/grade 3, and triple-negative cancers as IIIC; and all others as IIIB. Endpoints were breast cancer-specific survival (BCSS), overall survival (OS), and disease-free survival (DFS). We studied 885 patients in the MDA cohort and 338 in the SEER cohort. In the MDA cohort, the prognostic stage showed significant predictive power for BCSS, OS, and DFS (all p < 0.0001), although the anatomic stage did not. In both cohorts, the Harrell concordance index (C index) was significantly higher in the prognostic stage than the anatomic stage for all endpoints. In conclusion, the prognostic stage provided more accurate prognostication for IBC than the anatomic stage. Our results show that the prognostic staging is applicable in IBC.