The ACCENT group previously established disease-free survival (DFS) with 2 or 3 years median follow-up to predict 5 year overall survival (5yr OS) in stage II and III colon cancer. ACCENT further proposed (1) a stronger association between DFS and OS in stage III than II, and (2) 6 or 7 years necessary to demonstrate DFS/OS surrogacy in recent trials. The relationship between endpoints in trials with oral fluoropyrimidines, oxaliplatin, and irinotecan is unknown.
Associations between the treatment effect hazard ratios (HRs) on 2 and 3yr DFS, and 5 and 6yr OS were examined in 6 phase III trials not included in prior analyses from 1997-2002. Individual data for 12,676 patients were analyzed; two trials each tested oxaliplatin, irinotecan, and oral treatment vs 5-FU/LV.
Overall association between 2/3 yr DFS and 5/6 yr OS HRs was modest to poor (simple R2 measures: 0.58 to 0.76, model-based R2: 0.17 to 0.49). In stage III patients, the association increased (model-based R2≥0.79). Observed treatment effects on 2 yr DFS accurately 5/6 yr OS effects overall and in stage III patients.
In recent trials of cytotoxic chemotherapy, 2 or 3yr DFS HRs are highly predictive of 5 and 6yr OS HRs in stage III but not stage II patients. In all patients the DFS/OS association is stronger for 6yr OS, thus at least 6 year follow-up is recommended to assess OS benefit. These data support DFS as the primary endpoint for stage III colon cancer trials testing cytotoxic agents.
Funded by NCI Grant CA-25224 to the Mayo Clinic to support the North Central Cancer Treatment Group.