Delay in commencing adjuvant therapy for colorectal cancer seems to impair survival in some retrospective studies. This study was planned to evaluate its impact on survival. MethodsThis was a retrospective study enrolling patients registered from 2000 to 2012 in two large cancer-dedicated institutions in Brazil. The primary outcome was overall survival according to early vs late chemotherapy initiation. The interval between the primary surgery and the start of adjuvant chemotherapy was calculated. Survival was estimated using the Kaplan-Meier method and the impact of multiple prognostic factors on survival by Cox regression analysis. ResultsBy the end of 2012, a total of 1963 Stage II and III colorectal patients were identified and 1318 patients received adjuvant chemotherapy, with 22% and 46% of those starting adjuvant chemotherapy within 6weeks and 8weeks of surgery. The median period of follow-up was 41months. Patients starting chemotherapy within 6-8weeks of surgery had longer overall survival compared with those who started after (6weeks vs later, hazard ratio 0.76, 95% CI 0.57-0.99, P=0.046; 8weeks vs later, hazard ratio 0.74, 95% CI 0.59-0.93, P=0.011). In the multivariate analysis, age, stage, histological grade, angiolymphatic invasion, emergency surgery and preoperative therapy were independent prognostic factors, but the interval between surgery and start of adjuvant therapy was not. ConclusionIn this large retrospective study, the standard prognostic factors impacted on survival whereas the timing of adjuvant therapy did not. Patients with delayed adjuvant chemotherapy may have worse prognostic factors which could play a major role in their poor outcome.189871876