Background: The American Joint Committee on Cancer (AJCC) 8th edition staging system for breast cancer has been validated in the upfront surgery setting, but has not been examined for its prognostic impact on patients undergoing neoadjuvant chemotherapy.
Methods: The National Cancer Data Base was used to identify patients with invasive unilateral breast cancer from 2010 to 2015 who underwent neoadjuvant chemotherapy. AJCC clinical stage classification was compared between the 7th and 8th editions. Receiver operating characteristic analysis of Kaplan-Meier overall survival (OS) was used to determine the predictive fit of the 7th and 8th edition staging in estimating OS.
Results: AJCC 7th and 8th clinical staging assignments were applied to 57,466 patients who underwent neoadjuvant chemotherapy for stage I-III breast cancer from 2010 to 2015. Overall, 37.5% of patients were downstaged and 27.8% were upstaged from the 7th to the 8th edition classification. Kaplan-Meier curves comparing 7th and 8th edition staging differed in OS rates, with a mean follow-up time of 41.5 months. AJCC 8th edition prognostic staging was a better predictor of OS than 7th edition anatomic staging for both clinical stage [area under the curve (AUC) 0.67 vs. 0.62, p < 0.01] and pathological stage (AUC 0.70 vs. 0.66, p < 0.01).
Conclusions: Sixty-five percent of patients have a shift in clinical stage in the AJCC 8th edition. AJCC 8th edition staging has better predictive value for OS than 7th edition staging. While validation of these findings with an independent dataset is needed, 8th edition staging will help improve prognostic modeling in patients undergoing neoadjuvant chemotherapy.