Study: Marijuana use, testicular cancer may be linked

Seattle-Results of a population-based, case-control study suggest there may be an association between marijuana use and the occurrence of testicular germ cell tumors (TGCTs), researchers from the Fred Hutchinson Cancer Research Center and the University of Washington, Seattle, reported.

The data, published in Cancer (2009; 115:1215-23), showed a 70% increased risk of testicular cancer among patients who reported being marijuana smokers at the time of diagnosis, though the association might be limited only to nonseminoma malignancies.

"The only thing we can take away from this analysis is that we have uncovered a potentially interesting association between a commonly used drug and the risk of a very uncommon cancer," said Stephen M. Schwartz, MPH, PhD, professor of epidemiology, University of Washington. "We should not infer that marijuana use is a cause of testicular cancer, nor should we infer that it is even a risk factor for testicular cancer."

Risk of TGCT was notably elevated for current marijuana use that occurred at least weekly or that began in adolescence.

"We didn't expect the association would be limited to current users, although it was heartening that among current users, it was the men who used it most often who were at the highest risk," Dr. Schwartz said. "We also did not expect that the association would be limited to the risk for nonseminomas."

As for the potential biological mechanism by which marijuana use might have an effect on male reproductive organs, Dr. Schwartz said his group's thoughts in that area are "truly speculative." He cited past research showing the negative effects of marijuana use on male reproductive hormones and sperm function. Some of those effects, he said, could be consistent with the hypothesized role of reproductive hormones in adolescence in promoting testicular tumors initiated in utero.

The team's other idea, which Dr. Schwartz calls "even more speculative," is that endogenous substances that interact with cannabinoid receptors have favorable properties, such that they may tend to protect cells from malignancy. Marijuana may erode the favorable effects of those endogenous compounds.

In any event, Dr. Schwartz acknowledges that the current study may not be sufficient for clinicians to begin counseling young patients against marijuana use.

"If a urologist is treating a young man who is known to be a heavy marijuana user, there is no particular justification to counsel him to stop based on this one study," he said. "On the other hand, the evidence that marijuana use is not good for a man's reproductive hormone milieu or sperm quality is based on more than one study, and could be reason to counsel men to stop.

"Finally, the mere fact that we know almost nothing about the long-term health risks of marijuana use could be a reason to counsel men that they might want to consider the benefits of using this drug (which are known) versus the risks (which are essentially unknown)."

The investigators believe their study is the first to assess a possible association between the use of marijuana and testicular cancer.