It is relatively common in mammals that one testicle fails to descent into the scrotum from where they develop in the abdomen. Normally the testicles will have both descended by two months of age, after which there is little chance of further development. The undescended testicle is usually non-functional and the name for this condition is cryptorchidism.

To say your dog will get cancer because of this is factually incorrect, but your dog’s chances of developing cancer are greatly increased. In addition, the chances of recovery from cancer of an undescended testicle are slimmer than otherwise because of its proximity to other tissues. Because of this, your vet should recommend castration, which will involve routine removal of the normal testicle and an incision, possibly into the abdomen, to remove the undescended testicle.