The optimal time of starting adjuvant chemotherapy after curative surgery in patients with colorectal cancer

BACKGROUND: Postoperative adjuvant chemotherapy (AC) is now well-accepted as standard for high-risk stage II and stage III colorectal cancer (CRC) patients, however the optimal time to initiate AC remains elusive. METHODS: A comprehensive literature search was performed using the PubMed and Embase databases. The Hazard ratio (HR) with the corresponding 95% confidence interval (CI) was used as an effect measure to evaluate primary endpoints. All analyses were conducted using Stata software version 12.0 with the Random-effects model. RESULTS: A total of 30 studies were included in our study. Upon comparison on overall survival (OS), we identified that delaying the initiation of AC for > 8 weeks after operation was significantly associated with poor OS (HR: 1.37; 95% CI: 1.27—1.48; P < 0.01). The poor prognostic value of AC delay for > 8 weeks was not undermined by subgroup analysis based on region, tumor site, sample size and study quality. No obvious differences were observed in survival between AC within 5–8 weeks and ≤ 4 weeks (HR: 1.03; 95% CI: 0.96 -1.10; P = 0.46). Moreover, two studies both highlighted that the survival benefit of AC was still statistically significant when AC was applied 5–6 months after surgery compared with the non-chemotherapy group. CONCLUSIONS: Delaying the initiation of AC for > 8 weeks after surgery was significantly associated with poor OS. AC started within 8 weeks after surgery brought more benefits to CRC patients. There were no obvious differences in survival benefits between AC within 5–8 weeks and ≤ 4 weeks. Compared to patients not receiving AC after surgery, a delay of approximately 5–6 months was still useful to improve prognosis. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12885-023-10863-w.