Environment, cancer, and molecular epidemiology: air pollution.

Most cancers result from human interaction with the environment. As may be expected, air pollution is the most frequent factor responsible for environmental carcinogenesis due to natural exposures (such as air contamination, background radiation, and asbestos) or man-made pollution (e.g., smoking). A challenging problem in clinical epidemiology has been the nonuniform distribution of cancer among populations equally exposed to carcinogenic circumstances. Recent findings made available through the development of molecular biology techniques have provided new insights into cancer susceptibility. The wide variations in the uptake and ability to activate xenobiotics are key phenomena in environmental carcinogenesis. The intracellular DNA repair systems are probably responsible for the end result of neoplastic transformation or normalcy in the presence of carcinogenic encounters.