The association between Cannabis smoking and lung cancer: a systematic review.

<h4>Background</h4>The association between Cannabis smoking and lung cancer is unclear, and a systematic appraisal of this relationship has yet to be performed. Our objective was to assess the impact of Cannabis smoking on the development of premalignant lung changes and lung cancer.<h4>Methods</h4>Studies assessing the impact of Cannabis smoking on lung premalignant findings and lung cancer were selected from MEDLINE, PSYCHLIT, and EMBASE databases according to the following predefined criteria: English-language studies of persons 18 years or older identified from 1966 to the second week of October 2005 were included if they were research studies (ie, not letters, reviews, editorials, or limited case studies), involved persons who smoked Cannabis, and examined premalignant or cancerous changes in the lung.<h4>Results</h4>Nineteen studies met selection criteria. Studies that examined lung cancer risk factors or premalignant changes in the lung found an association of Cannabis smoking with increased tar exposure, alveolar macrophage tumoricidal dysfunction, increased oxidative stress, and bronchial mucosal histopathologic abnormalities compared with tobacco smokers or nonsmoking controls. Observational studies of subjects with Cannabis exposure failed to demonstrate significant associations between Cannabis smoking and lung cancer after adjusting for tobacco use. The primary methodologic deficiencies noted include selection bias, small sample size, limited generalizability, overall young participant age precluding sufficient lag time for lung cancer outcome identification, and lack of adjustment for tobacco smoking.<h4>Conclusion</h4>Given the prevalence of Cannabis smoking and studies predominantly supporting biological plausibility of an association of Cannabis smoking with lung cancer on the basis of molecular, cellular, and histopathologic findings, physicians should advise patients regarding potential adverse health outcomes until further rigorous studies are performed that permit definitive conclusions.