Testis cancer causes?

Dumb luck. A few rare genetic syndromes put you at risk and there's a slight family tendency. A make-no-sense article a few years back blaming exercise probably reflected reporting bias. If you have a cryptorchid testis and it's not been fixed when it should have been, the risk is much higher. White guys are at the greatest risk, no one knows why.
Not clear. We know there is increase risk of having testis cancer in boys born with undescended testis and if a father or brother had testis cancer. In Many cases there is no known causes. There is new data showing that muscle building supplements may cause testis cancer.