Frequent or long-term marijuana use may dramatically increase a man's risk of developing the most aggressive form of testicular cancer, a new study suggests.
Researchers at the Fred Hutchinson Cancer Research Center found that being a marijuana user at the time of diagnosis was linked with a 70 per cent increased risk of testicular cancer.
Men who smoked marijuana on a weekly basis and/or had smoked marijuana since their teenage years had double the risk of study subjects who never smoked pot.
According to the researchers, the link between marijuana and testicular cancer appears to be restricted to nonseminoma, cancer that grows rapidly and often strikes between the ages of 20 and 35.
Nonseminoma accounts for about 40 per cent of all testicular-cancer cases.
"What young men should know is that first, we know very little about the long-term health consequences of marijuana smoking, especially heavy marijuana smoking; and second, our study provides some evidence that testicular cancer could be one adverse consequence," study author Stephen M. Schwartz, an epidemiologist at the Hutchinson Center, said in a statement.
"So, in the absence of more certain information, a decision to smoke marijuana recreationally means that one is taking a chance on one's future health."
The findings, which included data from 369 men, are published in the online edition of the journal Cancer.
Since the 1950s, incidence rates of nonseminoma and seminoma have risen by three to six per cent per year in the U.S., Canada, Europe, Australia and New Zealand.
Seminoma is the more common, slower growing form of testicular cancer that strikes men in their 30s and 40s.
At the same time, marijuana use has also risen, which is one reason the researchers decided to study a possible link between the substance and the disease.
The researchers already knew that risk factors for testicular cancer include having a family history of the disease, undescended testes and abnormal testicular development.
Scientists believe that the disease develops in the womb, when fetal germ cells that eventually make sperm in adulthood fail to properly develop and are therefore vulnerable to malignancy.
Researchers believe that exposure to male sex hormones during adolescence and adulthood influences these cells to become cancerous.
"Just as the changing hormonal environment of adolescence and adulthood can trigger undifferentiated fetal germ cells to become cancerous, it has been suggested that puberty is a 'window of opportunity' during which lifestyle or environmental factors also can increase the risk of testicular cancer," senior author Janet R. Daling, also an epidemiologist at the Hutchinson Center, said in a statement.
"This is consistent with the study's findings that the elevated risk of nonseminoma-type testicular cancer in particular was associated with marijuana use prior to age 18."
Factors that further reinforce the researchers' hypothesis is the fact that chronic marijuana use is known to have multiple negative effects on reproductive pathways, particularly reduced sperm quality, lower testosterone levels and impotency.
Male infertility and poor semen quality are linked to an increased risk of developing testicular cancer.
Marijuana may also block a cannabinoid-like chemical produced by the male reproductive system that is thought to have a protective effect against cancer.
The researchers caution that they need to conduct further research to confirm their findings in larger populations.
