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Meta-Analysis
. 2015 Feb 15;136(4):894-903.
doi: 10.1002/ijc.29036. Epub 2014 Jun 30.

Cannabis Smoking and Lung Cancer Risk: Pooled Analysis in the International Lung Cancer Consortium

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Free PMC article
Meta-Analysis

Cannabis Smoking and Lung Cancer Risk: Pooled Analysis in the International Lung Cancer Consortium

Li Rita Zhang et al. Int J Cancer. .
Free PMC article

Abstract

To investigate the association between cannabis smoking and lung cancer risk, data on 2,159 lung cancer cases and 2,985 controls were pooled from 6 case-control studies in the US, Canada, UK, and New Zealand within the International Lung Cancer Consortium. Study-specific associations between cannabis smoking and lung cancer were estimated using unconditional logistic regression adjusting for sociodemographic factors, tobacco smoking status and pack-years; odds-ratio estimates were pooled using random effects models. Subgroup analyses were done for sex, histology and tobacco smoking status. The shapes of dose-response associations were examined using restricted cubic spline regression. The overall pooled OR for habitual versus nonhabitual or never users was 0.96 (95% CI: 0.66-1.38). Compared to nonhabitual or never users, the summary OR was 0.88 (95%CI: 0.63-1.24) for individuals who smoked 1 or more joint-equivalents of cannabis per day and 0.94 (95%CI: 0.67-1.32) for those consumed at least 10 joint-years. For adenocarcinoma cases the ORs were 1.73 (95%CI: 0.75-4.00) and 1.74 (95%CI: 0.85-3.55), respectively. However, no association was found for the squamous cell carcinoma based on small numbers. Weak associations between cannabis smoking and lung cancer were observed in never tobacco smokers. Spline modeling indicated a weak positive monotonic association between cumulative cannabis use and lung cancer, but precision was low at high exposure levels. Results from our pooled analyses provide little evidence for an increased risk of lung cancer among habitual or long-term cannabis smokers, although the possibility of potential adverse effect for heavy consumption cannot be excluded.

Keywords: Cannabis smoking; lung cancer; marijuana smoking; never smokers.

Figures

Figure 1
Figure 1
Forest plot of the association between cannabis smoking (habitual vs. nonhabitual) and lung cancer risk. Pooled, pooled OR according to a random effects model (p-heterogeneity = 0.17). Abbreviations: No.: Number; Exp.: Number exposed; CI: confidence interval. MSH-PMH study, The Mount Sinai Hospital-Princess Margaret Hospital Study; MSKCC study, The Memorial Sloan-Kettering Cancer Center Study; UCLA study, The University of California at Los Angeles Study.
Figure 2
Figure 2
Restricted cubic spline (5 knots) to explore nonlinear association between cannabis smoking and lung cancer risk in all subjects showing the fitted odds of being a case versus being a control under different exposure measurements: (a) Joint-equivalents per day; (b) Duration; (c) Joint-years. Gray area, 95% confidence interval. Each model was adjusted for age, sex, race, highest education, tobacco smoking status and packyears, and study.

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