Prognostic impact of body mass index stratified by smoking status in patients with esophageal squamous cell carcinoma

Background: As smoking affects the body mass index (BMI) and causes the risk of esophageal squamous cell carcinoma (ESCC), the prognostic impact of BMI in ESCC could be stratified by smoking status. We investigated the true prognostic effect of BMI and its potential modification by smoking status in ESCC. Methods: We retrospectively analyzed 459 patients who underwent curative treatment at a single institution between January 2007 and December 2010. BMI was calculated using the measured height and weight before surgery. Chi-square test was used to evaluate the relationships between smoking status and other clinicopathological variables. The Cox proportional hazard models were used for univariate and multivariate analyses of variables related to overall survival. Results: BMI,18.5 kg/m(2) was a significantly independent predictor of poor survival in the overall population and never smokers after adjusting for covariates, but not in ever smokers. Among never smokers, underweight patients (BMI,18.5 kg/m(2)) had a 2.218 times greater risk of mortality than non-underweight (BMI. 18.5 kg/m(2)) patients (P=0.015). Among ever smokers, BMI < 18 kg/m(2) increased the risk of mortality to 1.656 (P=0.019), compared to those having BMI > 18 kg/m(2). Conclusion: Our study is likely the first to show that the prognostic effect of BMI was substantial in ESCC, even after stratifying by smoking status. Furthermore, the risk of death due to low BMI would be significantly increased in never smokers. We believe that the prognostic impact of BMI is modified but not eliminated by the smoking status in ESCC.