Joint and independent effect of alcohol and tobacco use on the risk of subsequent cancer incidence among cancer survivors: A cohort study using cancer registries.

Drinking alcohol and smoking tobacco are major modifiable risk factors for cancer. However, little is known about whether these modifiable factors of cancer survivors are associated with subsequent primary cancer (SPC) incidence, regardless of the first cancer sites. 27,762 eligible cancer survivors diagnosed between 1985 and 2007 were investigated for SPC until the end of 2008, using hospital-based and population-based cancer registries. The association between drinking, smoking and combined drinking and smoking (interaction) at the time of the first cancer diagnosis and incidence of SPCs (i.e., all SPCs, alcohol-related, smoking-related and specific SPCs) was estimated by Poisson regression. Compared with never-drinker/never-smoker, the categories ever-drinker/ever-smoker, current-drinker/current-smoker and heavy-drinker/heavy-smoker had 43-108%, 51-126% and 167-299% higher risk for all, alcohol-related and tobacco-related SPCs, respectively. The interaction of drinking and smoking had significantly high incidence rate ratios (IRRs) for SPCs among ever-drinker/ever-smoker and current-drinker/current-smoker, although ever drinking did not show a significant risk. Ever-drinker/ever-smoker had also significantly higher IRRs for esophageal and lung SPCs than never-drinker/never-smoker. Among comprehensive cancer survivors, ever and current drinkers only had a SPC risk when combined with smoking, while ever and current smokers had a SPC risk regardless of drinking status. Heavy drinking and heavy smoking were considered to be independent additive SPC risk factors. To reduce SPC incidence, it may be necessary (i) to reduce or stop alcohol use, (ii) to stop tobacco smoking and (iii) dual users, especially heavy users, should be treated as a high-risk population for behavioral-change intervention.