Molecular mechanisms in cancer induction and prevention.

Chemical and physical carcinogens, present in our environment and encountered in a variety of occupations, produce damage to DNA. X-rays produced direct ionizations and indirect hydroxyl radical attack. UV light in the short wavelength is specifically absorbed by unsaturated bonds in DNA, RNA, and proteins. There are a number of genetic sites that are specifically affected by environmental agents, and an increased sensitivity is found in certain genetic diseases. The development of a fully malignant tumor involves the activation or altered expression of oncogenes or the inactivation of tumor-suppressor genes that control normal cellular development. Mutations in the p53 tumor-suppressor gene are common in diverse types of cancer and could perhaps provide clues to the etiology of some cancers and to the effect of various environmental and occupational carcinogens in cancer development. The fact that environmental factors are involved to a great extent in cancer suggest that cancer may be preventable. Experimental as well as epidemiological data indicate that a variety of nutritional factors can act as anticarcinogens and inhibit the process of cancer development and reduce cancer risk. The interaction of cells with a number of environmental and occupational genotoxic substances such as X-rays, UV light, and a variety of chemicals including ozone results in an enhanced generation of free oxygen radicals and in modified pro-oxidant states. A number of nutritional factors such as vitamins A, C, E, beta-carotene, and micronutrients such as selenium act as antioxidants and anticarcinogens. Certain hormones such as thyroid hormones enhance oxidative processes and act as a co-transforming factor in carcinogenesis.(ABSTRACT TRUNCATED AT 250 WORDS)