Association Between Marijuana Use and Cancer Risk: Study

Smoking marijuana is linked to developing testicular germ cell tumor; its relationship with other cancers and the consequences of higher levels of use are unclear, reports a new study. The findings of the study are published in the journal JAMA Network Open.// The association between marijuana use and the risk of developing different kinds of cancer remained largely unclear in this analysis of 25 studies. The available studies were limited by small numbers of participants with high levels of marijuana use, poor quantification of marijuana use, and the presence of other factors such as cigarette smoking, which could influence results. Long-term studies are needed to improve understanding of marijuana’s association with the risk of developing cancer.

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

Study Selection English-language studies involving adult marijuana users and reporting cancer development. The search strategy contained the following two 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.

Main Outcomes and Measures Rates of cancer in marijuana users, with ever use defined as at least one joint-year exposure (equivalent to 1 joint per day for one 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, five cohorts, and one cross-sectional) were included; few studies (n = 2) were at low risk of bias. In a 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.

Long-term studies in marijuana-only smokers would improve understanding of marijuana’s association with lung, oral, and other cancers.

Source-Newswise