(1) Background: The optimal timing of adjuvant chemotherapy (CT) in gastrointestinal malignancies is still a matter of debate. For colorectal cancer, it is recommended to start post-operative treatment within eight weeks. The objective of this study was to assess the clinical effects of starting adjuvant CT within or after 6-8 weeks post-surgery in colorectal, gastric, and pancreatic cancer. (2) Methods: MEDLINE, EMBASE, and the Cochrane Library were searched in December 2018. Publications comparing the outcomes of patients treated with adjuvant CT administered before (early) or after (delayed) 6-8 weeks post-surgery for colorectal, gastric, and pancreatic cancer were identified. The primary endpoint was overall survival (OS). (3) Results: Out of 8752 publications identified, 34 comparative studies assessing a total of 141,853 patients were included. Meta-analysis indicated a statistically significant increased risk of death with delayed CT (>6-8 weeks post-surgery) in colorectal cancer (hazard ratio (HR) = 1.27, 95% confidence interval (CI) 1.21-1.33; p <0.001). Similarly, for gastric cancer, delaying adjuvant CT was associated with inferior overall survival (HR = 1.2, 95% CI 1.04-1.38; p = 0.01). Conversely, the benefit of earlier CT was not evident in pancreatic cancer (HR = 1, 95% CI 1-1.01; p = 0.37). Conclusions: Starting adjuvant CT within 6-8 weeks post-surgery is associated with a significant survival benefit for colorectal and gastric cancer, but not for pancreatic cancer.
Keywords: adjuvant chemotherapy; colorectal cancer; gastric cancer; meta-analysis.; pancreatic cancer; timing.