Marijuana use may lead to an increased risk of developing testicular cancer according to a new US study, the third study to flag a potential link.
In a case-control study of more than 450 men, published in CANCER, researchers from the University of California found men with a history of using marijuana were twice as likely to have a particular type of cancer usually occurring in younger men.
Testicular cancer is the most common cancer diagnosed in young men aged between 15 and 45. The study found a link with a type of testicular cancer that carries a somewhat worse prognosis than other types.
The study comes as an Australian report, backed by the Victorian arm of the Australian Medical Association, recommends cannabis be decriminalised for people aged 16 and older.
“The findings are biologically plausible but there is no proven mechanism to link the pharmacology of marijuana to development of testicular cancer,” said Paul Pharoah, reader in Cancer Epidemiology at the University of Cambridge.
Professor Pharoah said while a two-fold increase in risk appears moderately strong, in absolute terms the increase in risk is small, amounting to 0.012% for all men in their late twenties.
However Jan Copeland, director of the National Cannabis Prevention and Information Centre at the University of New South Wales, said while the study had mixed findings on the patterns of the association, it is just one more avoidable risk factor for young men, given we already know smoking cannabis affects fertility.
“Given that there are cannabis receptors in the testes and smoking cannabis affects sperm development, it is not surprising that we are seeing evidence develop of its association with some types of testicular cancer,” Professor Copeland said.
She added that as the peak ages for the development of testicular cancer and cannabis use coincided in young adulthood, protecting health and fertility is just one more reason for this group not to smoke cannabis.
Ian Haines, adjunct clinical associate professor and senior medical oncologist at Monash University said the study sounds well-conducted, and raises further concerns about a possible causal link between cannabis use and the development of non-seminomatous germ cell tumours of the testis in young men.
“This is a relatively rare cancer and no other possible epidemiologic contributors to the incidence, apart from previous undescended testes, a family history and known HIV infection, would explain a link. Presumably these factors were controlled for in the study.”
Mark Frydenberg, professor of surgery at Monash University, said while the association has been made between cannabis use and testicular cancer, it does not prove causality.
“Nonetheless, on the weight of this evidence and the other journal articles mentioned, it would seem prudent that young men are warned of the potential association between marijuana use and testis cancer. They should be discouraged from cannabis use but also encouraged to practice testicular self examination and report any abnormal lumps as soon as possible to their GPs.”