Tar content of cigarettes in relation to lung cancer.

Although it is generally considered established that the risk of lung cancer is directly related to the tar content of cigarettes, an examination of the results of previous studies does not yield conclusive evidence in favor of the hypothesis. The authors evaluated this issue in a study of 881 cases of lung cancer and 2,570 hospital controls who were 40 to 69 years of age; data were collected by interview in hospitals in the United States and Canada from November 1981 to June 1986. For each year of smoking, cigarette brands were classified according to their tar content as published in regular Federal Trade Commission reports (from 1967 to 1985) or the Reader's Digest (from 1957 to 1966). Tar values for years for which there was no published information were estimated by interpolation. Smokers were divided, according to the tar content of their cigarette brands averaged over a specified period, into low (less than 22 mg/cigarette), medium (22-28 mg/cigarette), and high (greater than or equal to 29 mg/cigarette) tar smokers. When the average tar content was based on cigarettes smoked at least 10 years previously, the relative risk estimates for medium and high tar smokers compared with low tar smokers were 3.0 and 4.0 after control for potentially confounding factors, including the number of cigarettes smoked per day. The trend was significant (p = 0.002). The tendency for the risk of lung cancer to increase with increasing tar content was consistent among men and women. The results provide further support for the hypothesis that the tar content of cigarettes is directly related to lung cancer risk. However, the data were limited in that there were very few subjects whose lifetime tar exposure averaged less than 10 mg/cigarette.