Risk of Cancer

Though cannabis appears to have beneficial effects in supportive care for patients with cancer, smoked marijuana contains carcinogens, some of which are also present in smoked tobacco, thus suggesting that smoking marijuana has the potential to increase the risk of developing certain cancers.5 Data supporting this, however, are mixed.

Lung Cancer

A pooled analysis of 6 different case-control studies conducted in the United States, Canada, United Kingdom, and New Zealand found no significant association between the development of lung cancer with habitual marijuana users (odds ratio [OR], 0,96; 95% CI, 0.66-1.38), those who smoked 1 joint per day or more (OR, 0.88; 0.63-1.24), and those who smoked greater than or equal to 10 joint-years (OR, 0.94;95% CI, 0.67-1.32) compared with nonhabitual or nonusers.5 The lack of association remained for non-tobacco users, with no association of lung cancer with habitual marijuana compared with nonhabitual use (OR, 1.03; 95% CI, 0.51-2.08). These data were adjusted by tobacco smoking status, which is a frequent confounder in these studies. An earlier case-control study conducted in Africa did find an association between marijuana smoking and lung cancer after adjusting for tobacco smoking (OR, 2.4; 95% CI, 1.6-3.8), but all marijuana users were also tobacco users.6

Head and Neck Cancer

A meta-analysis of 9 different case-control studies found no association between cannabis smoking and head and neck cancer (OR, 1.02;95% CI, 0.91-1.1).7

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Testicular Cancer

A meta-analysis of 3 case-control studies did find an association between cannabis use and testicular cancer.8 Current use of cannabis (OR, 1.62;95% CI, 1.13-2.72) and 10-year marijuana use (OR, 1.50;95% CI, 1.08-2.09) significantly increased the risk of testicular germ cell tumors (TGCT) compared with never use. There was no association, however, with ever use or former cannabis use and TGCT. The data were insufficient to determine if there was an association with seminoma development.

Conclusions

Current evidence suggests that cannabis use, particularly as single synthetic cannabinoids, can be effective in preventing or treating CINV. New studies are needed, however, to compare cannabis with newer antiemetic agents, such as NK1 receptor antagonists, or regimens. Cannabis may also provide some cancer-related pain relief and reduce the use of opioids. The effect of cannabis on cancer-related anorexia or cachexia is less clear.

Cannabis smoking does not appear to increase the risk of lung or head and neck cancers, based on some case-control studies. Testicular cancer, however, may be associated with cannabis smoking. Patients should be counseled about this potential risk.

In vitro and animal model data suggest that cannabis may have anticancer activity, but data from studies in humans have not yet been reported.

Though cannabis may have some beneficial effects, it is important to remind patients that it is associated with adverse effects and can impair driving enough to increase the risk of car accidents.3 In addition, though some form of cannabis is legal in about 67 U.S. states, it is still not legal to the federal government.9 Cannabis (not including synthetic cannabinoids that were FDA approved) is not regulated by the FDA and therefore inconsistency in quality, dosing, and chemical constituents is a major limitation.

References

  1. Turgeman I, Bar-Sela G. Cannabis use in Palliative oncology: a review of the evidence for popular indication. Isr Med Assoc J. 2017;19:85-88.
  2. Abrams DI, Guzman M. Cannabis in cancer care. Clin Pharmacol Ther. 2015;97:1-12. doi: 10.1002/cpt.108
  3. Kramer JL. Medical marijuana for cancer. CA Cancer J Clin. 2015;65:109-122. doi: 10.3322/caac.21260
  4. Ettinger DS, Berger MJ, Aston J, et al. Antiemesis, Version 2.2018. NCCN Clinical Practice Guidelines in Oncology. Updated April 30, 2018.
  5. Zhang LR, Morgenstern H, Greenland S, et al. Cannabis smoking and lung cancer risk: Pooled analysis in the International Lung Cancer Consortium. Int J Cancer. 2015;136:894-903. doi: 10.1002/ijc.29036
  6. Berthiller J, Straif K, Boniol M, et al. Cannabis smoking and risk of lung cancer in men: a pooled analysis of three studies in Maghreb. J Thorac Oncol. 2008;3:1398-1403. doi: 10.1097/JTO.0b013e31818ddcde
  7. de Carvalho MF, Dourado MR, Fernandes IB, et al. Head and neck cancer among marijuana users: a meta-analysis of matched case-control studies. Arch Oral Biol. 2015;60:1750-1755. doi: 10.1016/j.archoralbio.2015.09.009
  8. Gurney J, Shaw C, Stanley J, et al. Cannabis exposure and risk of testicular cancer: a systematic review and meta-analysis. BMC Cancer. 2015;15:1897. doi: 10.1186/s12885-015-1905-6
  9. Mead A. The legal status of cannabis (marijuana) and cannabidiol (CBD) under U.S. law. Epilepsy Behav. 2017;70:288-291. doi: 10.1016/j.yebeh.2016.11.021