Frequent and/or long-term marijuana use may significantly increase a man's risk of developing the most aggressive type of testicular cancer, according to a new study.
The researchers from Fred Hutchinson Cancer Research Centre found that being a marijuana smoker at the time of diagnosis was associated with a 70% increased risk of testicular cancer. The risk was particularly elevated (about twice that of those who never smoked marijuana) for those who used marijuana at least weekly, and/or who had long-term exposure to the substance beginning in adolescence.
The results also suggested that the association with marijuana use might be limited to non-seminoma, a fast-growing testicular malignancy that tends to strike early, between ages 20 and 35, and accounts for about 40% of all testicular-cancer cases.
The study results were published in the journal Cancer.
Rise in testicular cancer incidence
Since the 1950s, the incidence of the two main cellular subtypes of testicular cancer, non-seminoma and seminoma – the more common, slower growing kind that strikes men in their 30s and 40s – has increased by 3% to 6% per year in the US, Canada, Europe, Australia and New Zealand. During the same time period, marijuana use in North America, Europe and Australia has risen accordingly, which is one of several factors that led the researchers to hypothesise a potential association.
"Our study is not the first to suggest that some aspect of a man's lifestyle or environment is a risk factor for testicular cancer, but it is the first that has looked at marijuana use," said author Stephen M Schwartz, an epidemiologist and member of the Public Health Sciences Division at the Hutchinson Centre.
Established risk factors for testicular cancer include a family history of the disease, undescended testes and abnormal testicular development. The disease is thought to begin in the womb, when some foetal germ cells (those that eventually make sperm in adulthood) fail to develop properly and become vulnerable to malignancy. Later, during adolescence and adulthood, it is thought that exposure to male sex hormones coaxes these cells to become cancerous.
Marijuana affects reproductive system
"Just as the changing hormonal environment of adolescence and adulthood can trigger undifferentiated foetal 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," said senior author Janet R Daling, an epidemiologist who is also a member of the Centre's Public Health Sciences Division. "This is consistent with the study's findings that the elevated risk of non-seminoma type testicular cancer, in particular, was associated with marijuana use prior to age 18."
Chronic marijuana exposure has multiple adverse effects on the endocrine and reproductive systems, primarily decreased sperm quality. Other possible effects include decreased testosterone and male impotency. Because male infertility and poor semen quality also have been linked to an increased risk of testicular cancer, this further reinforced the researchers' hypothesis that marijuana use may be a risk factor for the disease.
A lot of unanswered question
The researchers emphasise that their results are not definitive, but rather open a door to more research questions.
"Our study is the first inkling that marijuana use may be associated with testicular cancer, and we still have a lot of unanswered questions," Schwartz said, such as why marijuana appears to be associated with only one type of testicular cancer. "We need to conduct additional research to see whether the association can be observed in other populations, and whether measurement of molecular markers connected to the pathways through which marijuana could influence testicular cancer development helps clarify any association that exists," he said.
In the meantime, Schwartz said, "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," he said. "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." – (EurekAlert! February 2009)
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