Male fetuses of mothers exposed to radiation during early pregnancy may have a higher chance of developing testicular cancer, according to a new study from the University of Texas MD Anderson Cancer Center.

More than 8,500 new cases of testicular cancer are diagnosed in the United States each year, according to the American Cancer Society. The disease is increasingly prevalent in young Caucasian men. During the past 50 years, the incidence has tripled in that group throughout the world.

In one of the first studies to show an external cause for testicular cancer, research with mice shows the male fetuses of mothers exposed to radiation during early pregnancy may have a higher chance of developing the increasingly common form of cancer.

While there’s been no documented proof, scientists have long suspected endocrine disruptors (chemicals that alter the endocrine – or hormonal – system), may be the cause of testicular cancer. Fetuses are especially vulnerable to even small amounts of the substances, which are already known to cause developmental and cognitive issues.

When endocrine disruptors were introduced into a mouse strain with a high spontaneous incidence of testicular cancer — which should’ve made them more sensitive to cancer caused by environmental agents — the results showed no increase in testicular cancer.

But when researchers gave modest doses of radiation, which is a DNA-damaging agent, to female mice in the middle of their pregnancies, all the male offspring developed testicular cancer, compared to 45 percent of mice not exposed to radiation. The tumors were also more aggressive and had more sites of origin.

The doctors involved say these results suggest that DNA-damaging agents, rather than endocrine disruptors, should be examined as a factor in the increased prevalence of testicular cancer.

“Although radiation exposure of pregnant females has been declining and is unlikely to be responsible for this increase, we intend to follow this up with studies of DNA-damaging chemicals found in cigarette smoke and air pollution, to which exposures of pregnant women have been increasing,” said study senior author Marvin Meistrich, Ph.D., professor in MD Anderson’s Department of Experimental Radiation Oncology.

Study findings were in the journal PLoS ONE.