Reply to passive smoking and the use of noncigarette tobacco products in association with risk for pancreatic cancer

Dr. Gianfranco Delle Fave and colleagues raised the issue of obesity and pancreatic cancer. Considering the high prevalence of obesity and its associations with cancer, we agree that obesity could play a role as important as cigarette smoking in cancer etiology and public health. However, whether the lack of association between passive smoking and pancreatic cancer observed in our study1 was affected by missing information on obesity is debatable. We have observed that cigarette smoking, diabetes mellitus, heavy alcohol consumption, chronic pancreatitis, family history of pancreatic cancer, and dietary mutagen exposure are the most notable epidemiological risk factors for pancreatic cancer in our study population. Obesity was not included in any of these reports because information on body mass index (BMI) was not collected at the early stage of the study. Preliminary analysis of BMI data from 356 cases and 333 controls that are involved in the passive smoking study showed that obesity was significantly associated with increased risk of pancreatic cancer (adjusted odds ratio [OR], 4.00; 95% confidence interval [CI], 2.01–7.96). Obesity also showed a modulating effect on the association between active smoking and risk of pancreatic cancer, with an OR of 1.44 (95% CI, 0.96–2.16) for those with a BMI of <25, an OR of 1.33 (95% CI, 0.80–2.22) for those with a BMI of 25.1–30, and an OR of 4.00 (95% CI, 1.17–13.6) for those with a BMI of >30. However, the association between passive smoking and risk of pancreatic cancer was not affected by including obesity in the model (OR, 1.08; 95% CI, 0.59–1.97). Among 176 cases and 156 controls of never smokers, we performed subgroup analyses that showed an OR of 1.50 (95% CI, 0.75–3.01) for those with a BMI of <25, an OR of 1.23 (95% CI, 0.52–2.95) for those with a BMI of 25.1–30, and an OR of 0.97 (95% CI, 0.20–4.75) for those with a BMI of >30. Even though the sample size is small, these data do not support a confounding effect of obesity on the association between passive smoking and risk of pancreatic cancer. As the sample size increases in the ongoing study, the effect of obesity alone and in interaction with other factors on the risk of pancreatic cancer will be much better illustrated. Pancreatic cancer is a multifactorial disease. Other unidentified factors, such as dietary habits and genetic variations, could also modulate the effect of passive smoking on pancreatic cancer. We acknowledge the limitations of each individual study and concur with Dr. Capurso and colleagues that effect of obesity along with physical activity should be considered in any future assessment of risk for pancreatic cancer. Donghui Li PhD*, Manal M. Hassan MD, PhD*, * Department of Gastrointestinal Medical Oncology, University of Texas M. D. Anderson Cancer Center, Houston, Texas.