 Use of 13-cis RA for chemoprevention of head and neck cancer only has been published by Hong et al. Their cases included a variety of head and neck cancers that are known to be not a homogenous group. The risk of second primary is different for different primary sites. Therefore, the value of 13-cis RA in chemoprevention is not conclusively addressed. In our proposal, only oral cavity cancer is included and the result will be more convincing. The result could be the basis of further chemoprevention clinical trial or guideline for clinical practice. 