For people with one undescended testicle who develop cancer, the undescended testicle is the one that has the cancer 80% of the time. Since the descended testicle can develop cancer 20% of the time, removal of the undescended testicle is rarely performed anymore as it used to be. Careful examination of the testicles is important, especially in someone who has history of an undescended one.
Hope this helps!
Dr. B.