Get any groin or testicle pain evaluated by a doctor!
Testicular cancer is most prevalent in young men- 18-40, I believe.
My husband had to have one testicle removed last year because he was diagnosed with the cancer. He's been cancer-free since, and hopefully forever.
The symptoms were very mild- a recurring backache that he attributed to physical activity, and one testicle was slightly larger than the other.
If caught in the early stages, it is easily contained. If not, it kills.

A pain in the testicle may not be cancer, but wouldn't you rather be sure? If my husband hadn't been required to have a complete checkup for the adoption process we are going through, he would probably not have bothered to go for another year or more. That could have been a death sentence.

All the guys reading this, please take care of yourselves!