San Diego, CA: Smoking cannabis, even long-term, is not positively associated with increased incidence of lung-cancer, according to the findings of the largest population-based case-control study performed to date. Lead investigator Donald Tashkin of the David Geffen School of Medicine, Division of Pulmonary and Critical Care Medicine, at the University of California-Los Angeles, presented the results at the 2006 International Conference of the American Thoracic Society in San Diego. Investigators assessed the possible association between cannabis use and the risk of lung cancer in middle-aged adults (ages 18-59) living in Los Angeles. Researchers conducted interviews with 611 subjects with lung cancer and 1,040 controls matched for age, gender and neighborhood. Data was collected on lifetime marijuana use, as well as subjects' use of alcohol, tobacco and other drugs, diet, occupation, and family history of cancer. Investigators used a logistical regression model to estimate the effect of cannabis smoking on lung cancer risk, adjusting for age, gender, ethnicity, education, and cumulative tobacco smoking and alcohol use. "We did not observer a positive association of marijuana use -- even heavy long-term use -- with lung cancer, controlling for tobacco smoking and other potential cofounders," investigators concluded. Their data further revealed that one subset of moderate lifetime users (10-<30 "joint years") actually had an inverse association between cannabis use and lung cancer. The study did report a 20-fold increased risk in heavy tobacco smokers. The five-year trial was sponsored by the US National Institutes of Health (NIH). NORML Senior Policy Analyst Paul Armentano said that Tashkin's findings reaffirm the results of prior case-control studies dismissing a causal link between cannabis use and certain types of lung and upper aerodigestive tract (UAT) cancers. These include: a 2001 John Hopkins University hospital-based case-control study that found neither "lifetime use" nor "ever use" of cannabis were associated with head, neck or lung cancer in younger adults; a 2004 University of Washington case-control study that found "no association" between cannabis use and incidents of oral cancer, regardless of how long, how much or how often individuals had used it; and a 1997 Kaiser Permanente retrospective cohort study that found that cannabis use was not associated with increased risks of developing tobacco-use related cancers of the lung and upper aerodigestive tract or other cancers in men and women who used marijuana but did not smoke tobacco. "The most remarkable aspect of this study is that its findings are, in fact, unremarkable," Armentano said. "As has been previously reported by the US Institute of Medicine and others, there is no conclusive evidence that marijuana causes cancer in humans, including those cancers generally related to tobacco use." Armentano suggested that cannabis consumers who desire the rapid onset of action associated with inhalation but who are concerned about the potential harms of noxious smoke can dramatically cut down on their intake of carcinogenic compounds by engaging in vaporization rather than smoking.