Novel Postneoadjuvant Prognostic Breast Cancer Staging System.

Purpose: Prognostic staging after neoadjuvant chemotherapy (NACT) is not included in American Joint Commission on Cancer (AJCC) staging. This study addressed this deficiency by including responses to therapy with standardized staging variables in a validated prognostic staging system for patients treated with NACT.

Methods: The National Cancer Database was queried to identify 140,605 patients treated with NACT between 2010 and 2018. Three response categories (no response, partial response, and complete response [pCR]) were created on the basis of comparison of clinical and post-NACT pathologic staging. Univariate and multivariate analyses of clinical stage, estrogen receptor, progesterone receptor, human epidermal growth factor receptor 2 (HER2), and grade were analyzed for each category. Predictive models for each response category were validated using the bootstrap technique. Calibration plots compared predicted and observed 3-year survival probabilities in the training and validation data sets.

Results: Each validated model demonstrated statistically significant survival differences in the postneoadjuvant prognostic stage assignment. Of all patients with a pCR, 94.2% were assigned to postneoadjuvant ypStage I compared with 35.5% of patients with no response. Advancing clinical stage had a progressive but small impact on overall survival (OS) with pCR (high-grade, triple-negative breast cancer [TNBC]: cStage I, 97% v cStage IIIB/IIIC, 91%; grade 2 luminal A: 97% v 91%) but was associated with a profound decrease in OS with no response for TNBC or HER2+ disease (high-grade TNBC 89% v 50%) and less profound for grade 2 luminal A disease with no response (97% v 81%).

Conclusion: We present a novel, validated prognostic staging system that predicts OS according to the response to NACT. These data will provide AJCC stage assignments for a growing proportion of patients treated with NACT.