A proposal for a new classification of T4 breast cancer as stage IIIC: a report from the Korean Breast Cancer Society

The objective of this study is to investigate staging system of the stage IIIB and stage IIIC Breast cancer and determine the criteria for an update of the classification system. Since AJCC 6th edition, it is pointed out that stage IIIB showed a worse outcome compared with stage IIIC. Using information from two databases, including the nationwide Korean Breast Cancer Registry (KBCR), three cohorts composed of patients from the asan medical center from 1989 to 2002 (cohort I), from 2003 to 2008 (cohort II), and KBCR from 2003 to 2005 (cohort III) were assembled. New classifications were suggested that rearranged stage IIIB as T1-3N3 disease and stage IIIC as T4 any N disease. From the joint analysis of 9640, invasive breast cancer patients from cohorts I and II showed the stage IIIB group showed a significantly worse DFS (HR 10.4, 95 % CI 6.9–15.7) compared with the stage IIIC group (HR 7.2, 95 % CI 5.9–8.7). T4d breast cancer showed worse DFS than T4 abc breast cancer but not significant (p = 0.505). The survival of patients with T1N3 and T2N3 tumors was higher than the other groups, and patients with T4N3 tumors showed the worst survival outcomes in terms of DFS, CSS. Using new suggested classification, in cohort III, the stage IIIB HR for CSS was changed from 15.4 (95 % CI 10.6–22.1) in the AJCC 6th edition to 12.6 (95 % CI 10.1–15.6) in the proposed new staging system. The stage IIIC HR for CSS was changed from 13.3 (95 % CI 10.7–16.4) in the AJCC 6th edition to 18.9 (95 % CI 14.0–25.6) in the proposed new staging using stage I as a reference. Reclassification of T4 any N disease as stage IIIC and T1-3N3 disease as stage IIIB is appropriate.