From chimney sweeps to oncogenes: the quest for the causes of cancer
The relationship between a number of environmental factors, such as exposure to chemicals or ionizing radiation, and an increased risk for cancer has been noted for many years. The cancers that develop may be indistinguishable from each other, yet may be caused by totally unrelated factors. Researchers have looked for the common connection between these environmental factors and the cancer that results. It has been known for some time that genetic damage occurs from exposure to these factors, but the mechanism for inducing cancer has not been known. When oncogenes were recently discovered, the common mechanism became more clear. Protooncogenes are genes with normal cellular functions that regulate cell growth. The function can be altered by viruses, for example, resulting in an oncogene, which leads to abnormalities, such as the uncontrolled growth seen in tumors. It is theorized that other factors, such as radiation, can similarly alter these genes. In humans, approximately 50 oncogenes have been identified and a number have been isolated from specific cancers. A single mutation in one of the base pairs of the gene can cause this alteration, as can a rearrangement of the gene. Many copies may be produced in the same cell, resulting in uncontrolled cell growth. Specific genetic abnormalities are found often in certain types of cancer. Recent research has focused on isolating oncogenes from cells that have been exposed to radiation to show the connection between radiation and cancer. Thus far, the data support this theory of how radiation causes cancer. Other research concerning oncogenes and cancer is also being carried out. A greater understanding of the causative mechanisms of cancer will help the development of methods for preventing and treating the disease. (Consumer Summary produced by Reliance Medical Information, Inc.)
Publication Name: Radiology
Radon: is it a problem?
Radon-222, a naturally-occurring radioactive by-product of uranium-238, is present in all soils. It enters buildings in varying degrees of concentration as an odorless and colorless gas. As this substance breaks down it emits products called "radon daughters" that can be deposited in the lungs and may result in the development of lung cancer. In some homes, (e.g., in the area around Reading Prong, PA.) very high levels of radon have been recorded, noticeably in basements and poorly ventilated areas. Radon exposure, particularly in the home, is now considered a significant radiation hazard. The degree of risk from exposure to low levels of radon over a long period of time is not known. Occupational exposure to radon daughters occurs in such work settings as mines. Radon may be responsible for a large portion of the "spontaneous" lung cancer mortality figures (i.e., lung cancer deaths not attributed to known carcinogens). This hypothesis is supported by studies of Navajo uranium miners who have otherwise had a low incidence of lung cancer. However, the interplay of cigarette smoking and radon remains an unsettled question with some reports suggesting an increased risk of lung cancer in smokers who are exposed to radon (in mining occupations) and others suggesting that smoking may provide a protective effect against such radon exposure. Radon may account for 55 percent of the ionizing radiation that persons are exposed to; other common sources are medical X-rays and nuclear medicine procedures. Clearly further studies are necessary to determine the health risk of radon exposure in members of the general population, specific occupational groups and in smokers.
Publication Name: Radiology
Parallel analyses of individual and ecologic data on residential radon, cofactors, and lung cancer in Sweden
Contrasting national and individual risk estimates of lung cancer due to indoor radon exposure may not be accounted for by geographical latitude. Researchers in Sweden adjusted the confounding latitude factor and found agreement between individual and aggregated data for radon risk. Residential radon exposure in both data sets was associated with a risk of lung cancer. Large ecological studies may erroneously not disclose weak association unless the original bias is corrected.
Publication Name: American Journal of Epidemiology
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