<qa>  What is the hazard of developing second primary tumors in Taiwan?Hong et al studied the effects of 13-cis retinoic acid on patients with history of head and neck cancers 4. After treatment of head and neck primary cancers with either radiotherapy or surgery or both, 103 patients were randomized to receive either adjuvant 13-cis retinoic acid or placebo. In an update of this trial with 55 months of follow-up, 16 patients 31 in the placebo group had developed second primary tumors, whereas 7 patients 14 in the treatment group had developed second primary tumors p0.04 5. Betel quid chewing becomes increasingly popular in Taiwan. Exposure to both smoking and betel quid significantly increases the risk of oral cavity cancer6. The hazard of developing second primary tumors is high in this population, therefore, chemoprevention is worthy of trial. 