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.