Cannabis as an Anticancer Agent: A Review of Clinical Data and Assessment of Case Reports

Background: Pre-clinical studies have demonstrated the potential anticancer activity of cannabinoids, yet little clinical data exist to support this. Nearly 40% of patients with cancer using cannabis believe it will treat their cancer with numerous anecdotal reports shared online through social media platforms. Case reports have been published in peer-reviewed journals, but often lack key clinical information to validate anticancer claims.

Methods: We reviewed literature in PubMed and EBSCO databases that evaluated the relationship between cannabis or the endocannabinoid system and potential anticancer activity. We also reviewed online sources, books, and ClinicalTrials.gov for reports or studies on using cannabis as cancer treatment. All case reports published in peer-reviewed journals were compiled and appraised as weak, moderate, or strong based on the quality of evidence provided supporting an anticancer effect. Strong reports met three criteria; (a) active cancer at time of cannabis administration, (b) validated laboratory or radiographic responses were reported, and (c) cannabis used without concurrent anticancer treatments.

Results: Of the 207 pre-clinical articles reviewed, 107 (52%) were pre-clinical studies with original data. A total of 77 unique case reports described patients with various cancers (breast, central nervous system, gynecological, leukemia, lung, prostate, and pancreatic) using cannabis. Our appraisal showed 14% of the case reports were considered strong, 5% moderate, and the remaining 81% were weak. Ten percent of cases were in pediatric patients. Cannabidiol use was most often reported as the anticancer cannabinoid with daily doses ranging from 10 to 800 mg. Tetrahydrocannabinol use was reported in six studies, with doses ranging from 4.8 to 7.5 mg. Two small trials published data on survival in patients with recurrent glioblastoma multiforme.

Conclusion: This review of clinical data suggests most published, peer-reviewed case reports provide insufficient data to support the claim for cannabis as an anticancer agent, and should not be used in place of evidence-based, traditional treatments outside of a clinical trial. No strong clinical trial data exist to confirm the pre-clinical studies that suggest cannabinoids may have an anticancer benefit. Future studies exploring anticancer potential of cannabis in patients with metastatic cancers who have not responded to traditional therapy are needed.