Validation of the 8th AJCC prognostic staging system for breast cancer in a population-based setting.

OBJECTIVES: To validate the newly proposed American Joint Committee on Cancer (AJCC) prognostic staging system for breast cancer.

METHODS: Surveillance, epidemiology, and end results (SEER) database (2010-2014) was accessed. Cumulative incidence function was conducted (through assessment of sub-distribution hazard) according to both anatomical and prognostic stages. Likewise, Cox cause-specific hazard ratio with pairwise hazard ratio comparisons were also assessed for both anatomical and prognostic stages. Survival analyses according to both anatomical and prognostic staging systems were conducted through Kaplan-Meier analysis/log-rank testing.

RESULTS: A total of 209,304 patients with non-metastatic breast cancer and upfront surgical treatment were included. According to anatomical stages, pairwise Cox hazard ratio comparisons between different stages were significant (P < 0.0001) except between stage IIIB and stage IIIC, while according to prognostic stages, all pairwise hazard ratio comparisons between different stages were significant (P < 0.05). Sub-distribution hazard ratio (using breast cancer death as the primary failure endpoint and using other causes of death as competing causes of death) adjusted for age, race, and surgery was as follows: for the anatomical groups, it was 1.671 (95% CI 1.627-1.716; P < 0.0001) indicating increasing risk of death from breast cancer with increasing stage; however, for the prognostic groups it was 1.790 (95% CI 1.744-1.838; P < 0.0001) indicating increasing risk of death from breast cancer with increasing stage. C-statistic was assessed using breast cancer death as the dependent variable; and the findings for the two staging systems were as follows: anatomical staging: 0.767 (SE 0.004; 95% CI 0.759-0.776); prognostic staging: 0.814 (SE 0.004; 95% CI 0.807-0.822).

CONCLUSIONS: The current analysis showed an improvement in the discriminatory value for the prognostic staging system compared to the anatomical staging system and endorsed its routine use in clinical practice.