Agents and methods for chemoprevention and treatment of neoplasia are described, the agents including a selective inhibitor of inducible nitric oxide synthase and a combination of a selective inhibitor of inducible nitric oxide synthase and an inhibitor of cylcooxygenase-2 in a pharmaceutical composition. The agents and methods are used for chemoprevention and treatment of neoplasia including colorectal cancer and other cancers affecting epithelial cells throughout the body. The agents can also be used to treat the fibrosis that occurs with radiation therapy, as well as adenomatous polyps, including those with familial adenomatous polyposis (FAP).