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May 6, 2008 NEW YORK (Reuters Health) - The consistency of the smoking intensity pattern associated with eight types of smoking-related cancers suggests a general phenomenon, according to a study published in the April 15th issue of the American Journal of Epidemiology. These findings may provide clues about the molecular basis of smoking-related cancer risk, researchers in the U.S. and Finland suggest. Previous research demonstrated that the rate of bladder and lung cancer is directly related to exposure, up to 15 to 20 cigarettes a day, with excess relative risk (RR) rising with increasing intensity for equal total exposure. Beyond that level of smoking, however, there is an inverse exposure rate, the excess RR decreasing with increasing intensity. In other words, for a fixed number of pack-years (20 cigarettes a day for 10 years, for example, equals 10 pack-years), the researchers write, "smoking at a lower intensity for a longer duration was more deleterious than smoking at a higher intensity for a shorter duration." In the current study, Dr. Jay H. Lubin of the National Cancer Institute, Rockville, Maryland, and his colleagues extended the earlier findings by examining the effect of smoking on eight smoking-related cancers (bladder, esophagus, kidney, larynx, liver, lung, oropharynx and pancreas). By basing the data on a single prospective cohort, Finland's Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study (ATBC), Dr. Lubin's group removed possible participation bias. Between 1985 and 1988, the ATBC trial enrolled 29,133 men ages 50 to 69 years who smoked at least 5 cigarettes a day. Since this cohort included only smokers, the current researchers obtained appropriate age-specific cancer rates from other databases in Scandinavia. Results showed that cancers of the lung, bladder, oral cavity, pancreas and esophagus showed qualitatively and quantitatively comparable intensity effects related to cigarette smoking, indicating that the intensity pattern may have reflected a general phenomenon. The researchers conclude that the consistency of their results show "these patterns likely derived from both intensity-dependent molecular mechanisms and nicotine-related smoking behavioral factors." Copyright 2008 Reuters. Click for Restrictions.
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