Researchers say that young men who smoke marijuana weekly, or who have smoked from their teen years on, face twice the risk of developing nonseminona, an aggressive form of testicular cancer, the Guardian reported Feb. 9.

Researchers said the elevated risk compared to nonusers may be due to stimulation of immature testicular cells that can later become tumors. The testicles are one of the few organs in the body that have receptor sites for cannabinoids, the active ingredient in marijuana.

Increases in the number of testicular-cancer rates since the 1950s could be due to higher rates of marijuana use during the same time period, experts said.

Current marijuana users had an overall 70-percent increased risk of testicular cancer compared to nonusers.

"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 researcher Stephen Schwartz.

The study from researchers at the Fred Hutchinson Cancer Research Center was published online in the journal Cancer.