Gastrointestinal cancer: epidemiological data and premalignant lesions.

A variety of cancers develop in the gastrointestinal tract. Knowledge of the epidemiological risk factors and the premalignant changes associated with these cancers may help prevent or decrease the incidence of these malignancies. We enumerate the risk factors and discuss the premalignant lesions associated with each cancer in light of the many epidemiological and clinical studies important to practicing gastroenterologists.