A systematic review and meta-analysis assessing the impact of body mass index on long-term survival outcomes after surgery for colorectal cancer

Background The impact of body mass index (BMI) on long-term survival outcomes after colorectal cancer surgery is debated. Design A systematic literature review and meta-analysis was performed to compare long-term survival outcomes of patients of different BMI categories after colorectal cancer surgery. Results Of the 2588 articles screened, 56 articles met the inclusion criteria, reporting on 72,582 participants. Patients with BMI <18.5 had significantly worse overall survival [hazard ratio (HR) 1.91; P < 0.0001], cancer-specific survival (HR = 1.91; P < 0.0001), disease-free survival (HR = 1.50; P < 0.0001) and recurrence-free survival (HR = 1.13; P = 0.007) compared to patients with a BMI of 18.5–25. There was no significant difference between those with BMI 25–30 and 18.5–25 in overall survival, cancer-specific survival, disease-free survival and recurrence-free survival, except for the subgroup of patients with colon cancer where patients with BMI 25–30 had significantly improved overall survival (HR = 0.90; P = 0.05) and disease-free survival (HR = 0.90; P = 0.04). Patients with BMI >30 had significantly worse disease-free survival (HR = 1.05; P = 0.03) compared to patients with a BMI of 18.5–25, but no significant difference in overall survival, cancer-specific survival and recurrence-free survival. Patients with BMI >35 compared to 18.5–25 had significantly worse overall survival (HR = 1.24; P = 0.02), cancer-specific survival (HR = 1.36; P = 0.01), disease-free survival (HR = 1.15; P = 0.03) and recurrence-free survival for colon (HR = 1.11; P = 0.04) and rectal (HR = 4.10; P = 0.04) cancer. Conclusions Being underweight (BMI < 18.5) or class II/III obese (BMI > 35) at the time of colorectal cancer surgery may result in worse long-term survival outcomes, whereas being overweight (BMI 25–30) may improve survival in a subgroup of patients with colon cancer. Optimising BMI may preoperatively improve long-term survival after surgery for colorectal cancer.