Abstract P4-08-16: Validation of the AJCC eighth edition prognostic stage compared with the anatomic stage for breast cancer with a Japanese single-institutional cohort
Authors: Miyamoto H , Saita C , Onishi M , Goto R , Iwamoto N , Honda Y , Aruga T 
Published: May 2019

Background: The American Joint Committee for Cancer (AJCC) 8th edition cancer staging system for breast cancer incorporated biologic factors in addition to the 7th edition anatomic stage. We analyzed how the new AJCC 8th edition prognostic stage refined its stratification compared with the anatomic stage.

Methods: We reviewed the data of 4,134 patients with stage I to III breast cancer who underwent surgery at Tokyo Metropolitan Komagome Hospital between 2000 and 2016. The anatomic stage and prognostic stage were re-staged according to the AJCC 8th edition staging manual. Patients who received neoadjuvant chemotherapy or had bilateral breast cancer and those with unknown clinicopathologic factors were excluded. The 21-gene Oncotype DX breast recurrence score was not used for staging in this study.

Results: A total of 2,469 patients with a median follow-up of 4.7 years (range 0.1-15.5 years) were identified. According to the anatomic stage, there were 1,259 patients of stage IA, 132 of IB, 591 of IIA, 206 of IIB, 130 of IIIA, 14 of IIIB and 73 of IIIC. According to the prognostic stage, there were 1,610 patients of stage IA, 331 of IB, 236 of IIA, 73 of IIB, 85 of IIIA, 43 of IIIB and 27 of IIIC. Sixty-four patients (2.6%) could not be assigned using the new staging system for the presence of micrometastases in lymph nodes with tumors larger than 2 cm. The 5-year disease-free survival (DFS) rates according to the anatomic stage were 97.4% for stage IA, 97.1% for IB, 95.8% for IIA, 86.5% for IIB, 77.9% for IIIA, 49.2% for IIIB and 54.9% for IIIC. According to the prognostic stage, the 5-year DFS rates were 97.9% for stage IA, 92.9% for IB, 91.2% for IIA, 79.8% for IIB, 67.4% for IIIA, 53.3% for IIIB and 38.7% for IIIC. Compared with the AJCC anatomic stage, the prognostic stage was increased in 148 patients (6.2%) and decreased in 808 patients (32.8%). For those in whom the stage changed, the change was by one stage up or down in 463 (19.3%), by 2 stages up or down in 401 (16.7%) and by 3 stages up or down in 92 (3.8%). Of the 1,842 patients with hormone receptor (HR)-positive and human epidermal growth factor 2 (HER2)-negative (HR+/HER2-) disease, 40.5% (745/1842) of cases were downstaged, and 0.7% (1/1842) were upstaged.

Discussion: The AJCC 8th edition prognostic staging system provided more refined stratification than the anatomic stage. In the Japanese cohort, the proportion of the downstaging rate was higher than the upstaging rate, and the prognostic evaluation of HR+ patients in particular was improved.

Citation Format: Miyamoto H, Saita C, Onishi M, Goto R, Iwamoto N, Honda Y, Aruga T. Validation of the AJCC eighth edition prognostic stage compared with the anatomic stage for breast cancer with a Japanese single-institutional cohort [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-08-16.