Field carcinogenesis theory is commonly seen in

Smoking causes diffuse epithelial injury in the oral cavity, neck, esophagus and lung. Patients cured of squamous cell cancers of the lung and esophagus, oral cavity and neck are at risk (as high as 5% per year) of developing second cancers of the upper aerodigestive tract. Cessation of cigarette smoking does not markedly decrease the cured cancer patient&;s risk of second malignancy, even though it does lower the cancer risk in those who have never developed a malignancy. Smoking cessation may halt the early stages of the carcinogenic process (such as metaplasia) but it may have no effect on late stages of carcinogenesis. This "field carcinogenesis" hypothesis for upper aerodigestive tract cancer has made "cured" patients an impoant population for chemoprevention of second malignancies.Reference: Harrison; 19th edition