New study links accelerating cancer rates in young adults with cannabis use
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We have known for over a decade that cannabis use is linked to testicular cancer. This holds true not only for long-term use, but also for frequent use. This means that young men who get into heavy cannabis use can get themselves into trouble quickly.
—Jasleen Salwan, MD, MPH, FASAM
Cancer incidence in younger adults has been rising across multiple tumor types for more than a decade. Researchers have examined obesity, diet, environmental exposures, endocrine-disrupting chemicals, delayed childbearing, and lifestyle factors as possible contributors.
A new analysis highlighted by The ASCO Post has drawn attention because it links increasing cannabis exposure at the population level with rising rates of breast and testicular cancers in adolescents and young adults (AYAs). []
The findings are already generating debate among oncologists, largely because cannabis use continues to increase while alcohol consumption trends downward in some populations.
Related: Your patients think THC drinks are healthier than alcohol. Are they?What the study found
The investigators analyzed cancer incidence trends in younger patients based on US SEER data and Canadian cancer registry data. The study focused on breast cancer incidence in females aged 20 to 34 years and testicular cancer in males aged 15 to 39 years. []
The researchers compared trends in states with legalized cannabis against states without legalization. The results showed that breast cancer incidence increased by 26% in cannabis-legalizing states compared with 17% in non-legalizing states. Testicular cancer incidence increased by 24% vs 14%, respectively. []
Canadian data showed even larger increases during the study period. Breast cancer incidence rose by 35%, while testicular cancer incidence increased by 83%. []
Related: An unpleasant syndrome surfaces as cannabis use growsWhy researchers are concerned
Cannabis smoke contains many of the same carcinogenic compounds found in tobacco smoke, including polycyclic aromatic hydrocarbons. []
Jasleen Salwan, MD, MPH, FASAM, Addiction Medicine Consultant at Start Your Recovery, says, “Cannabis use, independent of tobacco use, is linked to head and neck cancers, including in younger age cohorts.” She further adds, “Testicular cancer, the most common non-blood cancer among men ages 15-35, is rising around the world. We have known for over a decade that cannabis use is linked to testicular cancer. This holds true not only for long-term use, but also for frequent use. This means that young men who get into heavy cannabis use can get themselves into trouble quickly.”
Discussing the risk in younger females, Dr. Salwan further clarifies, “In women, we are seeing emerging evidence that cannabis may increase the risk of breast cancer, though more research is needed to better control for confounding factors.”
Related: Can engaging in oral sex increase your risk of head and neck cancer?The findings are hypothesis-generating
But so far, the findings can’t be interpreted as direct proof that cannabis causes breast or testicular cancer. Dr. Salwan says, “While we can never assume causation based on correlation, we also know that it would be unethical to conduct a randomized controlled trial to study the health effects of long-term cannabis use. So, we have to extrapolate from the data we have.”
Critics of the study point out its limitations. For example, legalization status was used as a population-level marker for exposure. Individual patient cannabis use was not measured. The researchers did not have information on dose, duration, route of administration, age at initiation, product potency, tobacco co-use, or other cancer risk factors. []
In a counterpoint also published in The ASCO Post, Stacy D'Andre, MD, and Donald Abrams, MD, wrote, “This paper is hypothesis-generating only.” They advised interpreting the study conclusions with caution. [] For oncologists, the study is best viewed as an epidemiologic signal rather than definitive evidence.
The timing of the cannabis uptick is notable
Gallup reported in 2025 that 54% of US adults drink alcohol, the lowest level recorded in its long-running survey.[] Many clinicians report how patients are replacing alcohol with cannabis, often viewing THC as the safer option.
Related: Some of your patients are 'California sober'—what does it mean, and are they healthier for it?Dr. Salwan comments, “You should think of both alcohol and cannabis as carcinogenic for multiple organs of the body. When you replace one with another, you are not necessarily lowering your risk of cancer, or other adverse health outcomes.”
What about vaping? Dr. Salwan explains, “When it comes to lung cancer or head and neck cancer, smoking is probably the most dangerous route of ingestion. However, there is a lot that we do not know about vaping cannabis. While some people believe that vaporizing the pure cannabis plant, as opposed to a synthesized cartridge (as in a vape pen), is less dangerous, the reality is probably more complicated than that.”
Related: Play Now: The FDA says flavored vapes may help adult smokers quit for good. Not all physicians agree. How does your counseling stack up?Patient counseling
Dr. Salwan explains that oncology teams should ask every patient about cannabis consumption. She adds, “Many patients living with cancer use cannabis to boost their appetite. At the same time, cannabis can cause something called hyperemesis syndrome, which is a cyclical vomiting syndrome where people throw up so much they often end up in the hospital."
"They often get into a vicious cycle where they are too nauseated to eat, then use cannabis as an appetite booster, only to fall back into the vomiting loop again," Dr Salwan adds. "You do not want to add this on top of the potential nauseating side effects of immunotherapy or chemotherapy.”
For primary care physicians, cannabis use deserves a place in routine cancer risk assessment. Documentation should include frequency, route, product type, age at initiation, duration, and tobacco co-use. These discussions are especially relevant in younger patients, fertility counseling, survivorship care, and patients with breast or testicular cancer.