Prognostic Validation of the American Joint Committee on Cancer 8th Staging System in 24,014 Korean Patients with Breast Cancer

PURPOSE: The American Joint Committee on Cancer (AJCC) recently released the breast cancer staging system, 8th edition, which included additional four biologic factors. However, there has been no external validation of the prognostic value of the new stages with different population-based databases. METHODS: To validate the prognostic value of the new staging system in the Asian population, with a focus on Korean patients with breast cancer, we performed a retrospective study with data from the Korean Breast Cancer Society that included 24,014 patients with invasive ductal or lobular carcinoma who underwent surgery between January 2009 and January 2012 in Korea. The proportional differences were evaluated between the anatomic staging system (AJCC 7th edition) and the prognostic staging system (AJCC 8th edition, December 2017 published version). Comparisons of overall survival (OS) and disease-free survival (DFS) with Kaplan-Meier graphs and hazard ratios were also performed. RESULTS: Our analysis included 24,014 patients (median age, 50 years; range, 20–91 years). Stage I, II, and III disease accounted for 47.6%, 43.5%, and 8.9%, respectively, of anatomic stages and 61.8%, 27.6%, and 10.8%, respectively, of clinical prognostic stages. A total of 6,272 cases (26.1%) were upstaged, 4,656 (19.4%) were downstaged, and 13,086 (54.5%) remained unchanged. OS and DFS decreased in the order from prognostic stages IA to IIIC but did not change among the anatomic stage groups. CONCLUSION: Our data suggests that the prognostic staging system provides superior prognostic value to the anatomic staging system in Korean patients with breast cancer.