Abstract: Background and purpose: The American Joint Committee on Cancer (AJCC) 8th edition cancer staging manual introduced a new prognostic staging system for breast cancer incorporating biological markers in addition to traditional anatomical factors. The purpose of this study was to determine the clinical value of the 8th edition AJCC classification for breast cancer. Methods: The data from 222 recurrent or metastatic cases of breast cancer after operation were analyzed. Cancer staging was determined using the 7^th edition anatomical staging criteria including tumor (T), node (N) and metastasis (M), and was further evaluated using 8^th edition prognostic classification. We compared the two staging systems and their relations to prognosis. Kaplan-Meier and log-rank tests were used for univariate comparison of disease-free survival (DFS). Results: The percentages of ⅠA, ⅠB, ⅡA, ⅡB, ⅢA, ⅢB and ⅢC were 34 (15.3%), 0 (0.0%), 73 (32.9%), 26 (11.7%), 45 (20.3%), 4 (1.8%) and 40 (18.0%) according to AJCC 7th edition anatomical TNM staging system, respectively. The percentages of ⅠA, ⅠB, ⅡA, ⅡB, ⅢA, ⅢB and ⅢC were 47 (21.2%), 35 (15.8%), 55 (24.8%), 17 (7.7%), 25 (11.3%), 30 (13.5%) and 13 (5.9%) according to AJCC 8th edition prognostic staging system, respectively. The difference between the two staging groups was significant (P=0.000). Changes occurred mainly in the following categories: the 7^th edition ⅠA was divided into the 8^th edition ⅠA and ⅠB categories; ⅡA was divided into ⅠA, ⅠB and ⅡA; ⅡB was divided into ⅠA, ⅠB, ⅡA, ⅡB and ⅢA; ⅢA was divided into ⅠB, ⅡA, ⅡB, ⅢA, ⅢB and ⅢC; and both the 7^th edition ⅢB and ⅢC were divided into the 8^th edition ⅢA, ⅢB and ⅢC categories. There was statistically significant difference in DFS between stage groups according to both AJCC 7^th edition TNM and 8^th edition prognostic staging systems (P=0.002 and 0.001), and the DFS in ⅢB and ⅢC groups according to AJCC 8th edition prognostic staging system was more accurate compared with AJCC 7^th edition. Conclusion: The 8^th edition AJCC prognostic classification could exactly predict the prognosis of breast cancer.

Key words: Breast carcinoma, Staging system, Prognosis