Background: Although the effect of betel quid chewing and smoking on oral cancer has been well documented, both influences, dose and duration during life time, on multistate progression of oral pre-malignancy are hardly addressed.
Methods: By recruiting a group of male chewers from different occupation groups, we modeled the effects of both duration and quantity of betel quid chewing and smoking on annual incidence rate of developing leukoplakia and average dwelling times (ADTs) staying in leukoplakia and erythroleukoplakia.
Results: The annual incidence rate (per year) of leukoplakia was estimated as 0.35% (95% CI: 0.22-0.48%). The ADTs were 24 years for leukoplakia and 7 years for erythroleukoplakia. Annual incidence rate of leukoplakia with high consumption and long duration of betel quid and smoking was higher. Both quantity and duration of smoking and betel quid chewing play minor roles in the influence of ADT. The risks of developing oral cancer after 20 years of follow-up were 42.2% for leukoplakia and 95.0% for erythroleukoplakia.
Conclusion: The effects of betel quid chewing and smoking on multistate progressions between oral pre-malignancies were elucidated. These results can be applied to predict long-term risk of malignant transformation varying with different duration and quantity of betel quid and cigarette.