A new US study suggests there is a link between marijuana use and elevated risk of the most aggressive form of testicular cancer, with frequent and long term users having the highest risk.

The study was the work of researchers from the Fred Hutchinson Cancer Research Center in Seattle, Washington, and other centres in the US and is published early online in the journal Cancer.

The study results show that being a marijuana smoker at the time of diagnosis was linked to a 70 per cent higher risk of testicular cancer. For men who smoked marijuana at least once a week or who had been smoking it since their teens, the risk was about double that of a man who had never smoked it.

The results also showed that the link with marijuana use might only be with the most aggressive, fast growing form of testicular cancer, nonseminoma. This type of cancer usually develops in younger men between the age of 20 and 35, and accounts for approximately 40 per cent of all cases of testicular cancer.

The rate of testicular germ cell tumors (TGCTs) has been growing by about 3 to 6 per cent a year for the last 40 to 60 years in the United States, Canada, Europe, Australia and New Zealand, and coincides with a similar rise in the use of marijuana in North American, Europe and Australia.

There are two types of TGCT: the aggressive, fast growing form, nonseminoma, that generally strikes younger men, and the more common, slower form, that generally strikes men in their 30s and 40s.

Previous studies have already shown that regular and frequent use of marijuana affects the human endocrine and reproductive system, and in men this has been linked with reduced testosterone, lower sperm quality, and impotency. Male infertility and poor semen quality has also been associated with an increased risk of testicular cancer, so the researchers decided to investigate if there was a link between this type of cancer and use of marijuana.

Study author Dr Stephen M Schwartz, an epidemiologist and member of the Public Health Sciences Division at the Hutchinson Center, said in a press statement that:

“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.”

Known risk factors for testicular cancer include family history of the disease, having undescended testes, and problems with testicular development. There is a widely held theory that the disease starts in the unborn fetus, when fetal germ cells (the ones that go on to make sperm in adulthood) don’t grow properly and become vulnerable to becoming cancerous and that this is further exacerbated by male sex hormones later in life.

As senior author Dr Janet R Daling, another epidemiologist and member of the Hutchinson Center’s Public Health Sciences Division explained:

“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.”

“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,” she added.

Daling said she first got the idea for the study when she heard a talk eight years ago that showed the brain and the testes both had cellular receptors for tetrahydrocannabinol, or THC, the main psychoactive component of marijuana. Since then, she said, other studies have found other sites for these receptors, which are also located in the heart, uterus, spleen and immune system.

The reproductive system of men naturally produces a cannabinoid-like chemical that is thought to protect against cancer tumors, and Daling, Schwartz and colleagues suggested that perhaps marijuana interferes with this protective process.

For the population-based, case-control study, the researchers interviewed 369 Seattle-Puget Sound-area (in Washington State) men aged 18 to 44 years who were diagnosed with TGCT from January 1999 through January 2006 and asked them about their lifetime use of marijuana. Their responses were compared to the responses of 979 age-matched healthy controls who lived in the same area.

The men were also asked about other lifestyle habits such as smoking and alcohol consumption.

The results showed that even after ruling out the effect of these other lifestyle habits, and other risk factors such as family history of testicular cancer and undescended testes, use of marijuana was significantly and independently linked to higher risk of testicular cancer.

However, the researchers said they do not claim the results are definitive, the link is just a link, and does not prove cause. They want their findings to open a door to further research, as Schwartz explained:

“Our study is the first inkling that marijuana use may be associated with testicular cancer, and we still have a lot of unanswered questions.”

One question for example is why is marijuana use linked to only one type of testicular cancer? Schwartz said more studies were needed to examine whether the link appears in other populations, and whether it might be possible to find molecular markers that show the pathways through which the marijuana might be helping testicular cancer to grow.

The researchers’ next step is to look at the expression of cannabinoid receptors in both seminomatous and nonseminomatous tumor tissue from the patients in this study and look for genetic variations and signalling molecules that might suggest the underlying mechanism of cancer development.

In the meantime Schwartz said that young men should know that we don’t know enough about the long term effect of marijuana use, especially heavy use, but this study suggests there could be at least one serious consequence, and therefore, his message is:

“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.”

“Association of marijuana use and the incidence of testicular germ cell tumors.”

Janet R. Daling, David R. Doody, Xiaofei Sun, Britton L. Trabert, Noel S. Weiss, Chu Chen, Mary L. Biggs, Jacqueline R. Starr, Sudhansu K. Dey, Stephen M. Schwartz.

Cancer Early View, published online 9 Feb 2009.

DOI: 10.1002/cncr.24159

Click here for Abstract.

Sources: Journal abstract, Fred Hutchinson Cancer Research Center.

Written by: Catharine Paddock, PhD