British scientists said that they had found the first genes that are associated with testicular cancer, the commonest form of cancer for men between the ages of 15 and 45.
Telltale variants in chromosomes 5, 6 and 12 are linked with an increased risk of the disease, according to their study, which compared the genetic code of 730 men who had testicular cancer with that of healthy men.
Inheriting the basket of three factors boosts the risk of the cancer, called testicular gem cell tumour, by up to fourfold.
The study is published online in the journal Nature Genetics.
"We have known for some time that men whose father, brothers or sons had testicular cancer are much more likely to get it themselves and we have been searching for this genetic link," said one of the investigators, Elizabeth Rapley of the Institute of Cancer Research, in the southern English county of Surrey.
"We believe there are more (risk factors) still to be found and we are working on identifying the rest."
The three telltales lie near genes that nurture testicular cells which are precursors in sperm development.
Worldwide incidence of testicular cancer is 7.5 cases per 100,000 men, but the rates vary remarkably between countries and according to ancestry, the ICR said in a press release.
Why this is so is unclear. Inheritance, though, is a well-known risk factor and seems to be far higher than for other cancer types.
Studies have found that the risk to brothers of testicular cancer patients is eight to 10 times higher than the general population, while for fathers of patients, the risk is four to six times higher.
Testicular cancer is 99 percent curable if caught in its early stages, the ICR said.