Carcinogenesis is a chronic and multistep process that results in malignancy. Malignant cells acquire the ability to invade or metastasize. Metastasis is often the first evidence of malignant disease. During the continuum of carcinogenesis, therapeutic interventions can be used to arrest or reverse this process. This is known as cancer chemoprevention. Effective cancer chemoprevention should suppress or block the clinical manifestation of malignancies by treating lesions before clinical signs or symptoms arise.