Men who are less fertile than normal also have an increased risk of testicular cancer, according to a study published today in the British Medical Journal. But some researchers dispute the authors' suggestion that both problems stem from a single cause, perhaps hormone-mimicking chemicals in the environment.
Testicular cancer has become increasingly common in the past 50 years. The disease strikes one in every 20,000 U.S. men and is most prevalent between ages 20 and 40. Scientists aren't sure what causes testicle cancer, but one controversial hypothesis suggests that exposure to estrogenlike compounds in the womb can somehow disrupt a male embryo's hormonal balance and lead to testicular cancer and reduced fertility later in life.
To test the idea that the two share a common cause, epidemiologists Henrik Møller and Niels Skakkebaek of the Danish National Research Foundation in Copenhagen compared the number of children born to 514 Danish men with testicular cancer to the number fathered by 720 cancer-free men of the same age. The researchers also surveyed participants about their sexual habits, education, marital status, and their history of sexually transmitted diseases. A cancer patient was classified as having "low fertility" if the number of children he had fathered 2 years prior to his diagnosis was less than the median number of children born by the same date to the age-matched controls. The results showed that men in the "low fertility" category had double the risk of testicular cancer compared to those who had fathered more children. Those with testicular cancer had, on average, 0.5 fewer children than men without the disease.
The researchers say the results bolster the case for a common cause, such as so-called endocrine disrupters. But Jonathan Li, a reproductive toxicologist at the University of Kansas Medical Center in Kansas City, disagrees. He says researchers already knew that men with testicular cancer often have impaired testicular function, which could develop as a symptom of the disease years before cancer is diagnosed. He also says the number of children a man fathers may be a poor measure of his fertility, because people may have fewer children for reasons that the study's authors did not control for, such as the wish to have a small family. "This paper is provocative," says Li, "but it's not instructive."