Body mass index and colorectal cancer prognosis: a systematic review and meta-analysis

Colorectal cancer is one of the most common cancers worldwide. However, it is unclear what influence body mass index (BMI) has on colorectal cancer prognosis. We conducted a systematic review and meta-analysis of observational studies to examine the association of BMI with colorectal cancer outcomes. We searched MEDLINE and EMBASE databases from inception to February 2015 and references of identified articles. We selected observational studies that reported all-cause mortality, colorectal cancer-specific mortality, recurrence and disease-free survival according to BMI category. Random-effects meta-analyses were conducted to combine estimates. We included 18 observational studies. Obese patients had an increased risk of all-cause mortality [relative risk (RR) 1.14; 95 % confidence interval (CI) 1.07–1.21], cancer-specific mortality (RR 1.14; 95 % CI 1.05–1.24), recurrence (RR 1.07; 95 % CI 1.02–1.13) and worse disease-free survival (RR 1.07; 95 % CI 1.01–1.13). Underweight patients also had an increased risk of all-cause mortality (RR 1.43; 95 % CI 1.26–1.62), cancer-specific mortality (RR 1.50; 95 % CI 1.20–1.87), recurrence (RR 1.13; 95 % CI 1.05–1.21) and worse disease-free survival (RR 1.27; 95 % CI 1.13–1.43). Overweight patients had no increased risk for any of the outcomes studied. Both obese and underweight patients with colorectal cancer have an increased risk of all-cause mortality, cancer-specific mortality, disease recurrence and worse disease-free survival compared to normal weight patients.