The findings suggested that the higher-risk connection was only with nonseminoma, the most aggressive and fastest-growing type of testicular germ cell tumor (TGCT). It accounts for about 40 percent of TGCTs in the United States and usually strikes men aged 20 to 35. The more common, slower-growing variety of testicular cancer is generally found in men in their 30s and 40s.
The incidence of both types of tumor has been increasing by 3 percent to 6 percent annually during the last 40 to 60 years in the United States, Canada, Europe, Australia, and New Zealand, paralleling the rise in marijuana use in those regions.
Janet R. Daling, the paper’s senior author, said a lecture eight years ago gave her the idea for the study. The speaker revealed that the brain and the testes both had cellular receptors for tetrahydrocannabinol (THC), the active alkaloid in marijuana. More recent research has found these receptors to be also in the heart, uterus, spleen, and immune system. Daling is an epidemiologist and a member of the Hutchinson Center’s Public Health Sciences Division.
Men’s reproductive systems naturally generate a compound structurally similar to THC that may prevent tumors. Daling and her team theorized that marijuana may obstruct this protective process.
In the study, the scientists interviewed 369 Seattle-area men who were 18 to 44 years of age and who had been diagnosed with testicular cancer from January 1999 through January 2006. They questioned the patients about their lifetime use of marijuana, tobacco, and alcohol. The researchers also interviewed a control group of 979 healthy men of the same age, residing in the same area.
The doctors then ruled out the effects of the non-marijuana lifestyle habits, as well as factors known to increase testicular cancer risk, such as family history of the disease, undescended testes, and problems with testicular development. They concluded that marijuana smoking was appreciably and independently connected to a higher risk of TGCTs.
But Stephen M. Schwartz, another study author who is also an epidemiologist and a member of the Public Health Sciences Division at the Hutchinson Center, said in a news release that “we still have a lot of unanswered questions.” The link with marijuana use, he said, doesn’t prove that marijuana causes testicular cancer.
The team would like to investigate, for example, why marijuana is linked with an increased incidence of only one kind of TGCT, whether the link holds true for the general population, and what molecular pathways there might be in the marijuana-TGCT relationship.
In the meantime, Schwartz said, science knows so little about how marijuana affects the body that young men should approach its use – especially its heavy use – circumspectly. “In the absence of more certain information,” he said, “a decision to smoke marijuana recreationally means that one is taking a chance on one’s future health.”