I just went to a urologist to get one checked out a few weeks back and I would reccomend it. Its better than worrying if its cancer or not, all while telling yourself after the worry "its problably nothing."
As soon as he saw what I was talking about, the doc said it was problably a cyst, but had me go get an ultrasound for confirmation. The ultrasound confirmed that it was a cyst on the epididymus. Its amazing what they can see w/ an ultrasound. You can even see the bloodflow into each testicle, which can also help determine if you have cancer there or not..
Cysts aren't a serious problem (nothing warranting surgery in my case @ least) unless there are many of them and/or they get big enough to cause local discomfort.
Go get it checked out ASAP.