Last Updated: 2003-09-01 8:01:03 -0400 (Reuters Health)

NEW YORK (Reuters Health) - The risk of testicular cancer is established in large part by environmental exposures early in life, results of a new study suggest, although the researchers admit that at this point they aren't exactly sure what type of exposures increase the risk.

For at least 50 years, there has been an "unexplained" epidemic of testicular cancer in several populations, although there is a marked difference in the occurrence of the disease among countries, Dr. Anders Ekbom, of the Karolinska Hospital in Stockholm, Sweden, and associates explain in the Journal of the National Cancer Institute.

For example, the incidence of testicular cancer is roughly twice as high in Sweden as it is in Finland and Denmark. "These differences cannot be explained solely by genetic differences, but environmental exposures, particularly early exposures, have been implicated in the [development] of testicular cancer," according to the team.

To investigate further, Ekbom's group identified 93,172 Finnish men who immigrated to Sweden between 1969 and 1996. These immigrants were less likely to develop testicular cancer than the Swedish general population.

There was no link between age at immigration or duration of stay in Sweden and the reduced risk of testicular cancer.

"The findings are compatible with the hypothesis that lifetime risk of testicular cancer is determined early in life, possibly before birth," Ekbom and colleagues write.

"Although we are still without a good hypothesis regarding what exposures are associated with an increased incidence of testicular cancer, our results strongly implicate early exposures as major determinants," they say.