[Pre- and post-diagnosis body mass index in association with colorectal cancer death in a prospective cohort study]

Objective: To evaluate the association between pre-and post-diagnosis body mass index (BMI) and risk of colorectal cancer (CRC) death. Methods: The cohort consisted of 3, 057 CRC patients from Shanghai who were diagnosed from Jan. 1, 2009 to Dec. 31, 2011 and aged from 20 to 74 years. The pre- and post-diagnosis BMI and clinical and lifestyle factors were collected at baseline. Death information was collected using record linkage with the Shanghai Cancer Registry and telephone confirmation during follow-up by the end of 2019. The Cox proportional regression model was used to estimate HR with 95% CI. Results: Analysis by multivariable Cox model showed no association between pre-diagnosis BMI and death risk in both male and female patients. Male patients with a post-diagnosis underweight BMI had an elevated risk of death compared to those in normal weight (HR=1.69, 95% CI: 1.21-2.37), especially in early stage cases. Overweight patients (HR=0.74, 95% CI: 0.61-0.89) and patients with obesity class Ⅰ (HR=0.63, 95% CI: 0.45-0.89)had better survival with decreased risks of death, especially in advanced stage cases. The decreased death risk in patients with obesity class Ⅱ was not significant (HR=0.57, 95% CI: 0.24-1.39). The P(trend) value for decreased risk of death with increased BMI in female patients was statistically significant (P<0.001), and the overweight and obesity class Ⅰ categories had better survival in advanced stage(HR(overweight)=0.62, 95% CI: 0.42-0.93; HR(obesity class Ⅰ)=0.39, 95% CI: 0.16-0.98). Both male and female patients with post-diagnosis BMI loss >2.0 kg/m(2) had an increased death risk when compared with those with stable BMI (change≤1.0 kg/m(2)) between pre- and post-diagnosis. BMI gain after diagnosis did not change death risk. Conclusions: Post-diagnosis BMI in the overweight or obesity class Ⅰ groups might be conducive to prolonging male CRC patients' survival, while underweight might result in poor prognosis. Keeping weight and avoiding excessive weight loss should be suggested for all CRC patients after diagnosis.