Assessment of the Prognostic Staging System of American Joint Committee on Cancer 8th Edition for Breast Cancer: Comparisons with the Conventional Anatomic Staging System

Purpose: The 8th edition of the American Joint Committee on Cancer (AJCC) staging manual introduced a new prognostic staging system for breast cancer.This study aimed to evaluate the changes in staging distribution and predictive power of the new staging system.Methods: Of the 12,275 patients with breast cancer identified from the Severance Breast Cancer Registry who underwent surgery between 1978 and 2016, 12,125 patients met the inclusion criteria.Results: In both the 7th and 8th staging systems, stage I patients constituted the largest proportion (38.2% and 48.4%).Migration from the 7th to 8th edition of the AJCC manual resulted in a decrease in stage II population and an increase in stage I and III populations.A total of 1,293 (15.4%) patients were upstaged, and 1,201 (14.3%) were downstaged.Downstaged patients had better recurrence-free and overall survival (p < 0.001).Pathologic complete response after neoadjuvant therapy showed good prognosis as p stage 0, and yp stages I and III showed poorer outcomes than the same p stage (p < 0.001).Conclusions: Staging migrations are common in early breast cancer under the prognostic staging system.The prognostic staging system of the 8th edition of the AJCC manual discriminates survival outcomes better than the anatomical staging system of the 7th edition of the AJCC manual.