Lung cancer and type of cigarette smoked

Lung cancer risk in smokers of different types of cigarette was compared ba sed on evidence from 54 epidemiological studies, each of over 100 lung canc er cases. Random effects meta-analyses estimated the relative risk of lung cancer in filter and plain cigarette smokers ( or with most and least filte r use), in lower and higher tar smokers, in ever handrolled and manufacture d only smokers, and in ever black tobacco and blond tobacco only smokers. F rom 43 gender-specific estimates, the risk was estimated to be 36% (95% con fidence interval 27% to 44%) lower in filter than in plain cigarette smoker s. The reduction was evident in both genders and in different continents. I t was greater, 50% (33% to 63%, n = 11 estimates), for squamous-cell carcin oma 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 smoke rs. This reduction, seen in both genders, equates to a 2% to 3% risk reduct ion 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 critic ally on results from specific studies or the limited confounding adjustment in some studies. Various problems with the epidemiological evidence are di scussed, 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 contr ol for nonsmoking confounding variables. Difficulties also arise in adjusti ng appropriately for aspects of smoking behavior that not only may differ b etween 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, th at lung cancer risk is affected by the type of cigarette smoked. The sugges tion that the switch to low tar cigarettes has led to an increase in the sm oker/nonsmoker lung cancer relative risk and in the relative frequency of a denocarcinoma versus squamous carcinoma is shown to be weakly based. Althou gh more data are needed relating to modern very-low-tar cigarettes, the evi dence is consistent with tar reduction and the switch to filter cigarettes having reduced lung cancer risk. Indeed, the meta-analysis estimates may se riously understate the risk reductions associated with lifetime smoking of low-tar filter cigarettes.