Annual Scientific Meeting
Introduction: Metabolic risk factors have been implicated in the incidence of colorectal cancer (CRC); however, less is known about the relationship between obesity and CRC outcomes. We hypothesized that obesity would be associated with worse outcomes compared to normal weight, but with better outcomes compared to underweight individuals.
Methods: A systematic review of electronic databases was performed through May 2019, including NCBI, Embase, Cochrane, and Web of Science. Screening was performed independently by two authors using Covidence. Inclusion criteria were retrospective and prospective cohort studies reporting CRC outcomes at least 60 months after CRC diagnosis. The primary outcome analyzed was CRC mortality in obese compared to normal body mass index (BMI). Secondary outcomes included overall mortality, disease free survival (DFS) and CRC mortality by BMI category (underweight, normal, overweight, and obese), and high vs. normal waist circumference (WC). Odds ratios (OR) and 95% confidence intervals (95% CI) are reported. Random effects analysis was performed for all outcomes, with heterogeneity assessed by the I2 statistic and meta-regression by area of origin (East vs. West).
Results: 484 relevant citations were identified and 17 were included in the final analysis. Fifteen studies analyzed CRC outcome data in terms of BMI, and 2 in terms of WC. These studies comprised 251,347 patients, with a median age range of 61.8-71 years and follow-up time range of 60-192 months. Obesity was associated with significantly increased CRC-specific mortality compared to normal BMI (Figure 1). Interestingly, study origin (East vs. West) explained 53% of the heterogeneity in these results, R2=0.53 (Figure 2). Underweight patients had increased CRC mortality compared to both normal and overweight patients, but not significantly different from obese patients. High WC was also associated with increased CRC mortality compared to normal WC (Table 1). Obese and underweight patients both had increased OM compared to normal weight patients; underweight patients had increased OM compared to obese patients. Significant effects of BMI on DFS were only observed in Eastern studies, where underweight patients had worse DFS than normal weight and obese.
Discussion: Overweight and obesity as well as underweight are risk factors for CRC-specific mortality. Underweight patients had poorer prognosis than overweight patients, but not significantly different from obese patients.