It has been acknowledged that excess body weight increases the risk of colorectal cancer (CRC); however, there is little evidence on the impact of body mass index (BMI) on CRC patients' long-term oncologic results in Asian populations. We studied the influence of BMI on overall survival (OS), disease-free survival (DFS), and CRC-specific survival rates in CRC patients from the administrative claims datasets of Taiwan using the Kaplan-Meier survival curves and the log-rank test to estimate the statistical differences among BMI groups. Underweight patients (<18.50 kg/m2) presented higher mortality (56.40%) and recurrence (5.34%) rates. Besides this, they had worse OS (aHR:1.61; 95% CI: 1.53-1.70; p-value: < 0.0001) and CRC-specific survival (aHR:1.52; 95% CI: 1.43-1.62; p-value: < 0.0001) rates compared with those of normal weight patients (18.50-24.99 kg/m2). On the contrary, CRC patients belonging to the overweight (25.00-29.99 kg/m2), class I obesity (30.00-34.99 kg/m2), and class II obesity (≥35.00 kg/m2) categories had better OS, DFS, and CRC-specific survival rates in the analysis than the patients in the normal weight category. Overweight patients consistently had the lowest mortality rate after a CRC diagnosis. The associations with being underweight may reflect a reverse causation. CRC patients should maintain a long-term healthy body weight.
Keywords: body mass index; colorectal cancer; colorectal cancer-specific survival; disease-free survival; oncologic prognosis; overall survival.