Young men who began using marijuana as adolescents or who smoke pot at least once a week appear to be twice as likely to develop testicular cancer as those who never used the drug.
The association, as reported by researchers at the Fred Hutchinson Cancer Research Center in Seattle, was strongest with nonseminoma, an aggressive, fast-growing subtype of testicular cancer that typically strikes men between ages 20 and 35.
"It's not just that you develop testicular cancer, but you develop a worse type of testicular cancer," said Dr. Glen Justice, director of the cancer center at Orange Coast Memorial Medical Center in Fountain Valley, who was not involved with the study.
About 40% of testicular cancers are nonseminomas. The rest are slower-growing seminomas, which tend to occur a decade or two later, when men are in their 30s and 40s. Since the 1950s, both kinds have increased by 3% to 6% a year in the United States, Europe, Australia and New Zealand.
Various studies have looked for environmental or lifestyle changes that could account for the increase. The study published online today in the journal Cancer was the first to look at marijuana, its authors said.
Researchers interviewed 371 men ages 18 to 44 who had been diagnosed with testicular cancer. They interviewed an additional 979 men of the same age group and from the same three Washington counties who did not have cancer.
The researchers found a 70% higher risk of testicular cancer in those who were using pot at the time of diagnosis, with an even higher risk associated with younger age at first use and frequency of use. Hormonal changes during puberty are thought to make that a particularly vulnerable period for environmental influences.
The findings were independent of known risk factors, such as undescended testes and a family history of testicular cancer, and adjusted for cigarette smoking and alcohol use.
The senior author of the study, epidemiologist Janet R. Daling, got the idea to look at marijuana after learning that the testes, like the brain, have receptors for tetrahydrocannabinol, or THC, the chemical component of the marijuana high.
The researchers did not know why the association was seen with nonseminoma but not seminoma, because both subtypes have increased.Copyright © 2014, The Baltimore Sun