Study register · detailMeta-Analyse · Cancer Risk · 2021
Scoping Review and Meta-Analysis Suggests that Cannabis Use May Reduce Cancer Risk in the United States.
Clark et al.·Cannabis and cannabinoid researchImpact 2.5
MixedGRADEModerate10 citations
Samplek = 34 Studien n = 24 Pat.
Durationunclear
ControlNo cannabis use
EndpointRelative cancer risk
Blindingunklar
DesignMeta-Analyse
”Key finding
Non-significant trend towards reduced overall cancer risk (RR=0,90, p>0,06); after exclusion of selection and performance bias significantly reduced risk (RR=0,86, p<0,017); head and neck carcinomas showed significant risk reduction (RR=0,83), but high heterogeneity and low confidence in the results.
Summary
Scoping review with meta-analysis on cannabis use and cancer risk in the USA; k=34 studies (50 data points with risk ratios). Overall RR=0,90 (p>0,06, not significant, high heterogeneity I²=72,4%). After removal of studies with high selection/performance bias: RR=0,86 (p<0,017, Hedges g=0,66; N=24 data points), but still high heterogeneity (I²=74,9%). Testicular tumour: the only cancer type with RR>1 (RR=1,12, p=0,3, not significant). Head and neck carcinomas: negative association (RR=0,83, p<0,05, Hedges g=0,55). Data consistent with a negative association between cannabis use and non-testicular cancers, but low confidence due to high heterogeneity.
P
PopulationAdults in the USA with various cancers – pooled data from 34 studies, N=50 evaluable data points
I
InterventionCannabis use (various forms)
C
ControlNo cannabis use
O
OutcomeNon-significant trend towards risk reduction in the overall pool (RR=0,90, p>0,06); after bias adjustment significant risk reduction (RR=0,86, p<0,017); head and neck tumours: RR=0,83, p<0,05; testicular tumours: RR=1,12 (n.s.)
Confidence in the evidence
Very lowLowModerateHigh
Moderate
The third of four GRADE levels, the effect estimate is probably reliable.
Introduction:Cannabis smoke contains carcinogens similar to tobacco, in addition to compounds with antitumor activity. Cannabis use reduces the risk of obesity and cannabinoids inhibit chronic inflammation, known causes of cancer. The net effect of Cannabis use on cancer risk is not known. Objective: To examine the association between Cannabis use and cancer risk in the United States. Methods: Identify and analyze published data on cancer risk in Cannabis users. Results: A total of 55 data points, consisting of risk ratios of cancer in Cannabis users and nonusers, were identified from 34 studies. Of these, 5 did not contain data essential for inclusion in the meta-analysis. The remaining data showed a nonsignificant trend to an association with reduced risk (relative risk [RR]=0.90, p>0.06, N=50) although heterogeneity is high (I(2)=72.4%). Removal of data with high risk of selection bias (defined as those from North Africa and those that failed to adjust for tobacco) and data with high risk of performance bias (defined as those with fewer than 20 cases or controls among Cannabis users) resulted in an RR <1.0 (RR=0.86, p<0.017, N=24) and large effect size (Hedges g=0.66), but did not decrease heterogeneity (I(2)=74.9). Of all cancer sites, only testicular cancer showed an RR value >1, although this was not significant and had a negligible effect size (RR=1.12, p=0.3, Hedges g=0.02). Following removal of testicular cancers the remaining data showed a decrease in risk (RR=0.87, p<0.025, N=41). Cancers of the head and neck showed a negative association with cancer risk (RR=0.83, p<0.05), with a large effect size (Hedges g=0.55), but high heterogeneity (I(2)=79.2%). RR did not reach statistical significance in the remaining cancer site categories (lung, testicular, obesity-associated, other). The data are consistent with a negative association between Cannabis use and nontesticular cancer, but there is low confidence in this result due to high heterogeneity and a paucity of data for many cancer types.