Introduction:
It is not known whether adjuvant chemotherapy duration is non-linearly associated with postoperative mortality risk. This study was designed to examine this relationship in Chinese patients with colorectal cancer.

Material and methods:
This cohort study was conducted in 1171 participants with stage III and high-risk stage II colorectal cancer, who were treated in China between July 1, 2011, and September 1, 2018. The target independent variable was adjuvant chemotherapy duration, and the dependent variable was postoperative death.

Results:
After adjusting for confounding factors, an increase in adjuvant chemotherapy duration was negatively correlated with the risk of postoperative death (hazard ratio (HR) = 0.95, 95% confidence interval (CI): 0.900.99). However, a non-linear relationship between therapy duration and postoperative death was observed in the group with bolus and infused fluorouracil with oxaliplatin (FOLFOX). In this group, the incidence of death decreased only when chemotherapy duration was more than 14 weeks (HR = 0.78, 95% CI: 0.630.97). A stronger association between adjuvant chemotherapy duration and postoperative death was detected in the capecitabine and oxaliplatin (CAPOX) group (HR = 0.71, 95% CI: 0.55–0.94) compared with the FOLFOX group (HR = 0.96, 95% CI: 0.92–1.01).

Conclusions:
The duration of adjuvant chemotherapy with the FOLFOX regimen is associated with a non-linear reduction in postoperative deaths, which is only apparent after at least 14 weeks of treatment. However, patients with colorectal cancer may receive CAPOX adjuvant treatment for a longer duration.