Risk Factors for Early-Onset Colorectal Cancer: A Systematic Review and Meta-analysis

Despite the widespread increase in the incidence of early-onset colorectal cancer (EoCRC), the reasons for this increase remain unclear. The objective of this study was to determine risk factors for the development of EoCRC.We conducted a systematic literature review and meta-analysis of studies examining non-genetic risk factors for EoCRC, including demographic factors, comorbidities, and lifestyle factors. Random effects meta-analyses were conducted for risk factors that were examined in at least three studies. Heterogeneity was investigated using the Q-test and I2 statistic.From 3304 initial citations, 20 studies were included in this review. Significant risk factors for EoCRC included CRC history in a first-degree relative (RR 4.21, 95% CI 2.61-6.79), hyperlipidemia (RR 1.62, 95% CI 1.22-2.13), obesity (RR 1.54, 95% CI 1.01-2.35), and alcohol consumption (high vs. non-drinkers) (RR 1.71, 95% CI 1.62-1.80). While smoking was suggestive as a risk factor, the association was not statistically significant (RR 1.35, 95% CI 0.81-2.25). With the exception of alcohol consumption, there was considerable heterogeneity among studies (I2 > 60%). Other potential risk factors included hypertension, metabolic syndrome, ulcerative colitis, chronic kidney disease, dietary factors, sedentary behaviour, and occupational exposure to organic dusts, but these were only examined in one or two studies.The results of this study advance the understanding of the etiology of EoCRC. High-quality studies conducted on generalizable populations and that comprehensively examine risk factors for EoCRC are required to inform primary and secondary prevention strategies.