Marijuana use is gaining cultural acceptance as a way to ease discomfort in patients with cancer, but is it safety is still unclear.
There is growing acceptance of marijuana use to ease discomforts that arise from cancer and its treatments, including pain, anxiety and lack of appetite — especially since many US states have legalized the substance for medical and recreational use.
Yet, evidence that marijuana objectively helps these symptoms is slim, with much of the support for its use based on anecdotal reports.
This might seem to indicate that patients don’t have much to lose by trying marijuana. But there may be a serious downside associated with use of the drug: an increased risk of cancer.
A new review of studies conducted over more than four decades points to an association between long-term marijuana use and testicular cancer, although evidence of that connection is not definitive proof. Overall, the researchers found that “the association of marijuana use and cancer development remains unclear.”
Similar to Smoking Tobacco?
The review, published online by JAMA Network on Nov. 27, 2019, was a meta-analysis of 25 studies that considered marijuana use and any associated risk of developing lung or head and neck cancers, squamous cell or oral squamous cell carcinomas or testicular germ cell tumors. The research was led by Dr. Mehrnaz Ghasemiesfe of the Northern California Institute of Research and Education and the San Francisco Veterans Affairs Medical Center.
The researchers conducted the study to help determine whether using marijuana, like using tobacco, might constitute a preventable cause of cancer. They pointed out that marijuana and tobacco smoke share carcinogens, and that longer holding of breath during marijuana smoking leads to higher exposure to tar and carbon monoxide. They added that smoking marijuana is associated with bronchial inflammatory changes comparable to those that arise from smoking tobacco.
“Given that cancer is the second leading cause of death in the United States and smoking remains the largest preventable cause of cancer death (responsible for 28.6% of all cancer deaths in 2014), similar toxic effects of marijuana smoke and tobacco smoke may have important health implications,” they wrote.
The researchers also noted that two specific altered genes that promote the growth of cancer are found more frequently in the bronchial lining of marijuana-only smokers compared with tobacco-only smokers. On the other hand, they pointed out, the tetrahydrocannabinol (THC) in marijuana is known to fight some types of cancer.
As a result, they wrote, “The net association of marijuana use with developing cancer is unclear.”
Prolonged Marijuana Use Tied to Testicular Cancer
The review included studies of adults who’d had at least one “joint year’s” worth of exposure to marijuana; this meant they had used the equivalent of at least one marijuana joint per day for at least a year. Smoking was the predominant method of taking the drug. The studies were written in English and conducted between January 1, 1973 and June 11, 2018. Most of the studies compared a group of marijuana smokers with a group that did not smoke marijuana, looking retrospectively at their smoking patterns and health outcomes.
In a pooled analysis of three such studies, 10 years of marijuana use was associated with a 36% rise in the risk of testicular germ cell tumor and an 85% rise in the risk of nonseminoma testicular germ cell tumor. Participants’ exposure to marijuana in joint years was not reported in the studies.
People who responded positively when asked if they had ever used marijuana did not have an increased risk of cancer, according to the findings.
The researchers called the evidence about testicular cancer “low-strength.” In looking at studies of marijuana and the development of lung cancer, they found that evidence was insufficient because there were fewer participants who were marijuana-only smokers than those who smoked both marijuana and tobacco; there was minimal marijuana use among the study populations; and assessment of use was described poorly. Due to similar methodological problems in other studies in the review — including a generally younger age among marijuana users — potential ties between use of the drug and the development of other cancer types were “unclear,” the authors wrote.
“Long-term studies in marijuana-only smokers would improve understanding of marijuana’s association with lung, oral and other cancers,” they wrote.
Standardized tools to assess levels of marijuana use would help accomplish that, they stated.
“In the meantime, clinicians should discuss marijuana use with patients to raise awareness of the lack of clarity on potential clinically important harms and to debunk beliefs in unproven benefits,” the researchers concluded.
The study was funded by the National Heart, Lung, and Blood Institute of the National Institutes of Health and a National Cancer Institute grant to Memorial Sloan Kettering Cancer Center, in New York City.