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Abstract
Lung cancer risk in smokers of different types of cigarette was compared based on evidence from 54 epidemiological studies, each of over 100 lung cancer cases. Random effects meta-analyses estimated the relative risk of lung cancer in filter and plain cigarette smokers (or with most and least filter use), in lower and higher tar smokers, in ever handrolled and manufactured only smokers, and in ever black tobacco and blond tobacco only smokers. From 43 gender-specific estimates, the risk was estimated to be 36% (95% confidence interval 27% to 44%) lower in filter than in plain cigarette smokers. The reduction was evident in both genders and in different continents. It was greater, 50% (33% to 63%, n = 11 estimates), for squamous-cell carcinoma but was also evident, 20% (-6% to 39%, n = 8), for adenocarcinoma. The risk was 23% (12% to 32%, n = 22) lower for lower tar than higher tar smokers. This reduction, seen in both genders, equates to a 2% to 3% risk reduction per milligram tar per cigarette. The risk was increased by 42% (21% to 66%, n = 15) for handrolled cigarette smoking and 75% (47% to 109%, n = 12) for black tobacco cigarette smoking. These estimates did not depend critically on results from specific studies or the limited confounding adjustment in some studies. Various problems with the epidemiological evidence are discussed, including the difficulty of obtaining compatible exposure indices from each study, the inadequate reporting of data from the largest studies, the likelihood of misreporting of cigarette type, and the inadequate control for nonsmoking confounding variables. Difficulties also arise in adjusting appropriately for aspects of smoking behavior that not only may differ between those choosing to switch or not to switch to lower tar but also may change as a result of switching. The overall data clearly show, however, that lung cancer risk is affected by the type of cigarette smoked. The suggestion that the switch to low tar cigarettes has led to an increase in the smoker/nonsmoker lung cancer relative risk and in the relative frequency of adenocarcinoma versus squamous carcinoma is shown to be weakly based. Although more data are needed relating to modern very-low-tar cigarettes, the evidence is consistent with tar reduction and the switch to filter cigarettes having reduced lung cancer risk. Indeed, the meta-analysis estimates may seriously understate the risk reductions associated with lifetime smoking of low-tar filter cigarettes.