Prognostic analysis of N3 locally advanced breast cancer according to the 8th edition of AJCC clinical stage: a propensity-matched SEER analysis.

Abstract

Background: The 8th edition of the American Joint Committee on Cancer (AJCC) clinical staging-including both anatomical and prognostic staging-serves as a valuable tool for predicting the prognosis of N3 locally advanced breast cancer (LABC). This study aims to apply these criteria to analyze changes in staging and evaluate differences in survival outcomes.

Methods: Data from the Surveillance, Epidemiology, and End Results (SEER) database were used for patients with newly diagnosed N3 LABC and complete follow-up from 2010 to 2015. Patients were categorized into N3a, N3b, and N3c groups. Chi-squared tests compared differences, while univariate and multivariate Cox analyses assessed breast cancer-specific survival (BCSS) and overall survival (OS). Kaplan-Meier curves and the log-rank test were used to analyze prognostic factors. Propensity score matching (PSM) was applied to reduce baseline differences and enable further comparative validation.

Results: Before PSM, a total of 5,096 patients were included in this study. Among these patients were classified 4,080 as N3a, 655 as N3b, and 361 as N3c. Significant differences were observed among the three groups in terms of histological grade, tumour stage, estrogen receptor (ER) status, progesterone receptor (PR) status, human epidermal growth factor receptor 2 (HER2) status (all P<0.001). In Kaplan-Meier survival analysis stratified by anatomical staging, the N3b group had the most favourable prognosis, followed by the N3a and N3c groups (OS, P<0.001; BCSS, P<0.001). In prognostic staging, the N3b group had the most favourable prognosis, followed by N3a and N3c groups, for stages IIIb and IIIc (OS, P<0.005; BCSS, P<0.005). Multivariate Cox regression analysis identified that N-stage were significantly associated with prognosis (P<0.05). After PSM, 200 N3a patients, 118 N3b patients, and 287 N3c patients were included in this study. After PSM, Significant differences were observed among the three groups in terms of histological grade (P=0.04), tumor stage (P<0.001), ER status (P<0.001), and PR status (P<0.001). In Kaplan-Meier analysis stratified by anatomical staging, the N3b group had the best prognosis, followed by the N3a and N3c groups (OS, P=0.02; BCSS, P=0.07). In prognostic staging, for stage IIIb prognostic staging, the N3b group again exhibited the most favourable prognosis, followed by the N3a and N3c groups (OS, P=0.03; BCSS, P=0.12). Multivariate Cox regression analysis revealed that the survival risk in the N3b group is slightly lower than that in the N3a group.

Conclusions: In the anatomical and prognostic staging of N3 LABC, the N3b subgroup demonstrates the most promising prognosis. The 8th edition of the AJCC prognostic staging system offers a more detailed framework for assessing prognosis and guiding the diagnosis and treatment of N3 LABC.