Updated 5-year survival and exploratory T x N subset analyses of ACTS-CC trial: a randomised controlled trial of S-1 versus tegafur-uracil/leucovorin as adjuvant chemotherapy for stage III colon cancer

Objective Adjuvant Chemotherapy Trial of TS-1 for Colon Cancer (ACTS-CC), a randomised phase III trial, demonstrated that adjuvant therapy with S-1 for stage III colon cancer was non-inferior in 3-year disease-free survival (DFS) to that of tegafur-uracil plus leucovorin (UFT/LV). We updated DFS and overall survival (OS) and performed T x N subset analysis Methods A total of 1518 patients with curatively resected stage III colon cancer were randomly assigned to receive S-1 (80–120  mg/day on days 1–28 every 42 days, four courses) or UFT/LV (UFT: 300–600  mg/day and LV: 75  mg/day on days 1–28 every 35 days, five courses) Results The 5-year DFS rates of the S-1 and UFT/LV group were 70.2 % and 66.9 %, respectively (HR 0.88; 95%  CI 0.74 to 1.06; p=0.177), and non-inferiority of DFS was reconfirmed with a median of 63.5-month follow-up. The similarity of OS was also confirmed (HR 0.92; 95%  CI 0.72 to 1.17; p=0.488); 5-year OS rates of the S-1 and UFT/LV group were 86.0 % and 84.4 %, respectively. No significant interactions were identified between the major baseline characteristics and DFS of the S-1 and UFT/LV groups, except for histological type; S-1 was more favourable in patients with poorly differentiated adenocarcinoma. Patient outcomes were well separated by TNM-substages (IIIA/IIIB/IIIC). With the patients divided into 20 subsets by T and N factors, the DFS and OS rates of T3 and N1 subset, which accounted for 62 % of stage IIIB patients and 44 % of all studied subjects, were significantly better than those of the other subsets in stage IIIB and similar to those of stage IIIA. Conclusions Adjuvant therapy of S-1 for stage III colon cancer was reconfirmed to be non-inferior in DFS to those of UFT/LV after long follow-up. No difference in OS was also demonstrated. T3N1 patients might be considered separately from other patients included in stage IIIB because of its favourable outcome. Trial registration number NCT00660894.