Tags:  Medical cannabis; Cancer; Marijuana; Oncology.

 

The problem: Cancer is the second leading cause of death in the United States, and tobacco smoking has been identified as the leading preventable cause of cancer death. Despite popular belief, marijuana and tobacco share many carcinogens including reactive oxygen species and aromatic hydrocarbons, some of which and are even found in higher concentrations in marijuana. Studies have also identified several carcinogenic mechanisms unique to marijuana.

 

Why do this study? Rates of cannabis consumption in the USA continue to increase, and even though several studies have found potential relationships between cannabis consumption and the risk of developing several cancers, there is no definite relationship. This study aims to examine all the published evidence regarding the association between chronic cannabis consumption (defined as 1 joint/day for 1 year) and the development of various types of cancer.

 

The study: An exhaustive literature search was performed, searching for studies that report cancer development in marijuana users. A total of twenty-five studies were identified and included in the study. These studies examined the relationship with lung cancer (n=8), head and neck cancer (n=9), urogenital cancers (n=7) and other cancers (n=4). Evidence strength was insufficient to draw conclusions in all types of cancer except for head and neck squamous cell carcinoma (HNSCC) or testicular cancer (TGCT), which had a low strength of evidence. A meta-analysis of 4 case-controlled studies regarding HNSCC and cannabis use revealed no association between marijuana use and development of cancer (OR 1.26; 95% CI: 0.88-1.80). For testicular cancer, the analysis showed an increased risk of cancer development with more than 10 years of marijuana consumption (OR 1.36; 95% CI: 1.03-1.81).

 

Conclusions:  The main conclusion of this study is the positive association between testicular cancer and long term cannabis consumption (>10 years), as well as the additional finding of no association of cannabis and head and neck cancer.

 

What does this study add? Even though there are several potential mechanisms related to cannabis and cancer, the published evidence does not determine a clear association. This study determines that there is not enough high-quality evidence in this matter, and highlights the need for new, well designed long term follow up studies.

 

Funder:  This article was supported by grant 1R01HL130484-01A1 from the National Heart, Lung, and Blood Institute of the National Institutes of Health (Dr Keyhani). Dr Korenstein’s work was supported in part by Cancer Center Support Grant P30 CA008748 to Memorial Sloan Kettering Cancer Center from the National Cancer Institute.

 

Author conflicts: 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.

 

Commentary: (David Casarett MD). This study is useful in part because it underscores the findings of previous studies that haven’t found an association between cannabis and HEENT cancer.  The finding of an association with testicular cancer is interesting, because it’s consistent with some anecdotal data that some oncologists have flagged.  Although the mechanism of that association isn’t clear, given the high rates of cannabis use in younger men, it’s something that deserves further study, and perhaps caution.