Study: Marijuana use linked to increased risk of testicular cancer

WASHINGTON, Feb. 9 (Chinese media) -- 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 results of a study published on Monday in the online edition of the journal Cancer.

The researchers at Fred Hutchinson Cancer Research Center found that being a marijuana smoker at the time of diagnosis was associated with a 70 percent 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 nonseminoma, a fast-growing testicular malignancy that tends to strike early, between ages 20 and 35, and accounts for about 40 percent of all testicular-cancer cases.

Since the 1950s, the incidence of the two main cellular subtypes of testicular cancer, nonseminoma and seminoma -- the more common, slower growing kind that strikes men in their 30s and40s -- has increased by three percent to six percent per year in the United States, 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 hypothesize 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 Center.

The male reproductive system naturally produces a cannabinoid-like chemical that is thought to have a protective effect against cancer. The authors speculate that marijuana use may disrupt this anti-tumor effect, which could be an explanation for the possible link between marijuana and increased risk of testicular cancer.

The researchers emphasize that their results are not definitive, but rather open a door to more research questions. In future studies the researchers plan to measure the expression of cannabinoid receptors in both seminomatous and nonseminomatous tumor tissue from the cases in the study, and to see whether variation in the genes for the receptors and other molecules involved in cannabinoid signaling influences the risk of testicular cancer.