Background: The American Joint Committee on Cancer (AJCC) recently updated its breast cancer staging system to incorporate biological factors, including estrogen and progesterone receptor (ER, PR), and HER2 status, in the new “prognostic stage” in addition to the traditional TNM anatomic stage. For the clinical anatomic staging, IBCs are classified at T4d; N0-2 as IIIB; and N3 as IIIC. For the clinical prognostic staging, ER+/PR+/HER2+/grade1-2 staged as IIIA; ER+/PR-/HER2-/grade3, ER-/PR+/HER2-/grade3, and all triple-negative cancers staged as IIIC; and all others as IIIB. We undertook this study to validate the clinical prognostic and anatomic stages for inflammatory breast cancer (IBC), an aggressive subgroup. The prognostic staging system, which was developed using non-IBC data, has not been validated in IBC.

Methods: We established two cohorts of IBC patients diagnosed without distant metastasis: (1) patients treated at MD Anderson Cancer Center between 1989 and 2017 (MDA-cohort) and (2) patients registered in the SEER database between 2010 and 2015 (SEER-cohort). Survival endpoints including overall survival (OS), and disease-free survival (DFS) were calculated by the Kaplan-Meier method. Breast cancer-specific survival (BCSS) was calculated by the competing risk analysis. The log-rank test was used to compare differences in endpoints between staging groups. The Harrell concordance index (C index) was used to quantify staging models’ predictive performance. A higher C index indicates a better predictive performance.

Results: We studied 885 patients in the MDA cohort and 338 in the SEER cohort. In the MDA cohort, the prognostic stage upstaged 248 patients (28%) and downstaged 146 (16%) comparing with the anatomic stage. The prognostic stage showed significant predictive power for BCSS, OS, and DFS (all P<0.0001), although the anatomic stage did not. The C index was significantly higher in the prognostic stage than the anatomic stage for BCSS (0.643 vs. 0.526, P<0.0001), OS (0.641 vs. 0.533, P<0.0001) and DFS (0.599 vs. 0.494, P<0.0001). In the SEER cohort, the prognostic stage upstaged 117 patients (27%) and downstaged 73 (17%). The survival differences between staging groups were more prominent with prognostic stage than with anatomic stage. The C index was significantly higher in the prognostic stage than the anatomic stage for BCSS (0.685 vs. 0.550, P=0.0028) and OS (0.681 vs. 0.557, P=0.0008). In both cohorts, prognostic stage IIIA patients had the best survival rates with the 5-year BCSS of 83% in the MDA cohort and 100% in the SEER cohort.

Conclusions: The prognostic stage incorporating biological factors provided more accurate prognostication for IBC patients than the anatomic stage. Our results show that the 8th edition AJCC prognostic staging system is optimal for prognostification in IBC.

Citation Format: Kumiko Kida, Kenneth R Hess, Bora Lim, Toshiaki Iwase, Sudpreeda Chainitikun, Maryanne E Sapon, Vicente Valero, Anthony Lucci, Carisa Le-Petross, Wendy A Woodward, Savitri Krishnamurthy, Gabriel N Hortobagyi, Debu Tripathy, Naoto T Ueno. Validation of prognostic stage and anatomic stage in the American joint committee on cancer 8th edition for inflammatory 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 P5-06-10.