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Meta-Analysis
. 2019 Nov 1;2(11):e1916318.
doi: 10.1001/jamanetworkopen.2019.16318.

Association Between Marijuana Use and Risk of Cancer: A Systematic Review and Meta-analysis

Mehrnaz Ghasemiesfe  1   2 , Brooke Barrow  3 , Samuel Leonard  1 , Salomeh Keyhani  4   2 , Deborah Korenstein  5   6
Affiliations
Meta-Analysis

Association Between Marijuana Use and Risk of Cancer: A Systematic Review and Meta-analysis

Mehrnaz Ghasemiesfe et al. JAMA Netw Open. .

Erratum in

  • Error in Table 1.
    [No authors listed] [No authors listed] JAMA Netw Open. 2020 Jan 3;3(1):e1921065. doi: 10.1001/jamanetworkopen.2019.21065. JAMA Netw Open. 2020. PMID: 31940033 Free PMC article. No abstract available.

Abstract

Importance: Marijuana use is common and growing in the United States amid a trend toward legalization. Exposure to tobacco smoke is a well-described preventable cause of many cancers; the association of marijuana use with the development of cancer is not clear.

Objective: To assess the association of marijuana use with cancer development.

Data sources: A search of PubMed, Embase, PsycINFO, MEDLINE, and the Cochrane Library was conducted on June 11, 2018, and updated on April 30, 2019. A systematic review and meta-analysis of studies published from January 1, 1973, to April 30, 2019, and references of included studies were performed, with data analyzed from January 2 through October 4, 2019.

Study selection: English-language studies involving adult marijuana users and reporting cancer development. The search strategy contained the following 2 concepts linked together with the AND operator: marijuana OR marihuana OR tetrahydrocannabinol OR cannabinoid OR cannabis; AND cancer OR malignancy OR carcinoma OR tumor OR neoplasm.

Data extraction and synthesis: Two reviewers independently reviewed titles, abstracts, and full-text articles; 3 reviewers independently assessed study characteristics and graded evidence strength by consensus.

Main outcomes and measures: Rates of cancer in marijuana users, with ever use defined as at least 1 joint-year exposure (equivalent to 1 joint per day for 1 year), compared with nonusers. Meta-analysis was conducted if there were at least 2 studies of the same design addressing the same cancer without high risk of bias when heterogeneity was low to moderate for the following 4 cancers: lung, head and neck squamous cell carcinoma, oral squamous cell carcinoma, and testicular germ cell tumor (TGCT), with comparisons expressed as odds ratios (ORs) with 95% CIs.

Results: Twenty-five English-language studies (19 case-control, 5 cohort, and 1 cross-sectional) were included; few studies (n = 2) were at low risk of bias. In pooled analysis of case-control studies, ever use of marijuana was not associated with head and neck squamous cell carcinoma or oral cancer. In pooled analysis of 3 case-control studies, more than 10 years of marijuana use (joint-years not reported) was associated with TGCT (OR, 1.36; 95% CI, 1.03-1.81; P = .03; I2 = 0%) and nonseminoma TGCT (OR, 1.85; 95% CI, 1.10-3.11; P = .04; I2 = 0%). Evaluations of ever use generally found no association with cancers, but exposure levels were low and poorly defined. Findings for lung cancer were mixed, confounded by few marijuana-only smokers, poor exposure assessment, and inadequate adjustment; meta-analysis was not performed for several outcomes.

Conclusions and relevance: Low-strength evidence suggests that smoking marijuana is associated with developing TGCT; its association with other cancers and the consequences of higher levels of use are unclear. Long-term studies in marijuana-only smokers would improve understanding of marijuana's association with lung, oral, and other cancers.

Trial registration: PROSPERO identifier: CRD42018102457.

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Conflict of interest statement

Conflict of Interest Disclosures: Dr Keyhani reported receiving grants from the National Institutes of Health during the conduct of the study. Dr Korenstein reported receiving grants from the National Cancer Institute during the conduct of the study and reported that her spouse serves on the scientific advisory board of Vedanta Biosciences and does consulting work for Takeda. No other disclosures were reported.

Figures

Figure 1.
Figure 1.. PRISMA Diagram of Evidence Search and Selection
The flow of articles in the systematic review is shown. PRISMA indicates Preferred Reporting Items for Systematic Reviews and Meta-analyses; ROB, risk of bias. aThe number of full texts included in the literature review exceeds 25 because some studies were assigned to more than 1 outcome label and are counted twice.
Figure 2.
Figure 2.. Association Between Marijuana Use and Risk of Developing Head and Neck Squamous Cell Carcinoma (HNSCC) and Oral Cancer in Case-Control Studies
Included are 4 studies,,, for HNSCC and 2 studies, for oral cancer. The size of the boxes represents the weight of each study, and the diamond represents the overall effect. OR indicates odds ratio.
Figure 3.
Figure 3.. Association Between Marijuana Use and Risk of Developing Testicular Germ Cell Tumor (TGCT) in Case-Control Studies
Included are 3 studies.,, The size of the boxes represents the weight of each study, and the diamond represents the overall effect. OR indicates odds ratio.
See this image and copyright information in PMC

References

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