New Zealand represents an ideal country in which to study the association between cannabis and respiratory tract cancer. New Zealand has a high rate of cannabis use, and it is rarely mixed with tobacco within the joint as is the custom in the United Kingdom. New Zealand has among the highest rates of lung cancer worldwide with the indigenous Maori population having the highest incidence of any ethnic group.
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While cannabis smoking (defined as lifetime use of ≥20 joints) was not associated with a significantly increased risk of lung cancer (Table 3), those with the highest tertile of use (>10.5 joint-years of exposure) had a significantly increased risk, RR=5.7 (95% CI 1.5 to 21.6), after adjustment for age, sex, ethnicity, pack-years of cigarette smoking and a family history of lung cancer. Using the prevalence of the highest tertile of cannabis smoking of the controls we estimated that about 5% of lung cancer in those aged 55 years and under in New Zealand may be attributable to cannabis smoking.
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This population-based case-control study provides evidence of a relationship between smoking cannabis and lung cancer in young adults. For each joint-year of cannabis exposure the risk of lung cancer was estimated to increase by 8%.
CANNABIS USE AND RISK OF LUNG CANCER: A CASE-CONTROL STUDY (PCI, Aug. 14, 2008)