Stacy D’Andre, MD
Donald Abrams, MD
The conclusions drawn from the study by Johnson et al1 appear overstated and should be interpreted with caution. In the study discussed in this issue of The ASCO Post, investigators compared breast and testicular cancer incidence trends in American states that had or had not legalized the use of cannabis, as well as cancer incidence trends vs cannabis use in Canada. An association between the legalization of cannabis and increased cancer rates does not prove causality.Many factors may play a role in the increased cancer rates observed in adolescent and young adult patients, including the consumption of processed and ultraprocessed foods, sedentary behavior, increased obesity rates, environmental exposure, alterations in the gut microbiome, and exposure to known carcinogens, including tobacco and alcohol.2,3
The current study evaluates data at the population level and does not measure actual cannabis exposure. Were the patients with breast and testicular cancer using cannabis? In states in which cannabis is medically legal, patients obtain cannabis products at medical dispensaries, and they must be over 18 and have a medical certification. Hence, it is more likely that the duration of exposure to processed and ultraprocessed foods, accounting for 62% of caloric intake in younger Americans, provided a longer period of exposure to carcinogens than cannabis in the 15-year-old boys and 20-year-old women at the lowest age range included in this report. The timeframe in which these cancers developed was very rapid:if cannabis were a potent carcinogen, a multiyear or multidecade lag time would be expected before a large spike in population-level cancer diagnoses. Interestingly, if cannabis is in fact an endocrine disruptor, that would mean the increased breast cancers observed are triple negative.
Cannabis Use and Non-Seminoma Germ Cell Tumors
The National Academies of Sciences, Engineering, and Medicine (NASEM) concluded that there was limited evidence of a statistical association between cannabis use and non-seminoma germ cell tumors.4 However, who smokes cannabis? Young men. Who gets testicular cancer? Young men. Therefore, it is a statistical association and does not imply causation. It is similar to an observation that there might be more skin cancers in places where açaí bowls are consumed: true, true, and unrelated. A later study from the UK Biobank found no link between cannabis use and testicular cancer, but the number of participants in that study was too small to make a meaningful conclusion.5 That study reported a decreased risk of renal and bladder cancer in women using cannabis. The comments here that cannabis is associated with the development of 25/41 cancers really does harken back to the film Reefer Madness of almost 100 years ago. Although the NASEM study found only moderate evidence of no statistical association between the use of cannabis and the development of lung and oropharyngeal cancers,4 the Gallagher study examined the large percentage of people diagnosed with cannabis use disorder who also smoked tobacco and drank alcohol.6 Both, contrary to Dr. Johnson’s comment, are associated with significantly more cancer than cannabis.
…we agree that cannabis should not be consumed by most young adults, but to deprive patients living with and beyond cancer of the benefits of this safe and versatile botanical on the basis of alarmist evidence seems unnecessary.— Stacy D’Andre, MD and Donald Abrams, MD
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The authors point to a study allegedly showing a negative interaction between cannabis and immunotherapy.This study has been criticized for methodological issues,7 and subsequent studies have not demonstrated worse outcomes or altered immunomodulatory effects in patients on immunotherapy using cannabis vs nonusers.8-10More prospective studies are warranted, and caution may be best, especially in patients with cancer being treated with immune checkpoint inhibitors in the curative setting.
Observational Finding
This paper is hypothesis-generating only. It is an interesting observational finding, but the conclusions overstate the possible role of cannabis as a carcinogen, and the study did not track actual patient use longitudinally.Future studies are needed that control for confounders such as diet, obesity, lifestyle factors, and exposures. In the meantime, we agree that cannabis should not be consumed by most young adults, but to deprive patients living with and beyond cancer of the benefits of this safe and versatile botanical on the basis of alarmist evidence seems unnecessary.
DISCLOSURE: Dr. D’Andre and Dr. Abrams reported no conflicts of interest.
REFERENCES
1. Johnson RH, Speckhart A, Chien F, et al: Emerging evidence links cannabis use to increased risk of breast and testicular cancer in young Americans. Acad Oncol. June 5, 2025. (published online).
2. Jayakrishnan T, Ng K: Early-onset gastrointestinal cancers: A review. JAMA 334:1373–1385, 2025.
3. Ugai T, Sasamoto N, Lee HY, et al: Is early-onset cancer an emerging global epidemic? Current evidence and future implications. Nat Rev Clin Oncol 19:656-673, 2022.
4. National Academies of Sciences, Engineering, and Medicine. The health effects of cannabis and cannabinoids: The current state of evidence and recommendations for research. https://nap.nationalacademies.org/catalog/24625/the-health-effects-of-cannabis-and-cannabinoids-the-current-state. Accessed June 3, 2026.
5. Huang J, Huang D, Ruan X, et al: Association between cannabis use with urological cancers: A population-based cohort study and a mendelian randomization study in the UK biobank. Cancer Med 12:3468-3476, 2023.
6. Gallagher TJ, Chung RS, Lin ME, et al: Cannabis use and head and neck cancer. JAMA Otolaryngol Head Neck Surg 150:1068-1075, 2024. Erratum in: JAMA Otolaryngol Head Neck Surg. Published online February 27, 2025.
7. Piper BJ, Tian M, Saini P, et al: Immunotherapy and cannabis: A harmful drug interaction or reefer madness? Cancers (Basel)16(7):1245, 2024.
8 Behling-Hess C, Simonson G, Salz T, et al: The impact of cannabis on immune checkpoint inhibitor therapy: A systematic review of immunomodulatory effects of cannabis in patients with and without cancer. Support Care Cancer 33:166, 2025, https://doi.org/10.1007/s00520-025-09218-x.
9. Coschi CH, Ding K, Tong J: Effects of cannabinoids on immune checkpoint inhibitor response: CCTG pooled analysis of individual patient data. Immunotherapy 17:257-268, 2025.
10. Yao S, Li C-S, Gada U, et al: The impact of cannabis use on patient outcomes post immune checkpoint inhibitor (ICI) therapy in a longitudinal observational trial: The DiRECT Cohort. J Clin Oncol 4:12081, 2025.
Dr. D’Andre is Assistant Professor of Oncology, Mayo Clinic, Rochester, Minnesota. Dr. Abrams is Professor Emeritus of Medicine, University of California San Francisco.
