I'm 17. How do I go about telling my parents I have testicular cancer?

A year and a half ago I noticed my right testicle was a little swelled. I didn't know what to think of it and passed it off as just an irregular size. Recently I heard a story from my mom who described a kid in basically the same situation, who didn't tell his parents about the tumor and eventually did, then had it removed after it made its way to his lungs.

I'm certain it has progressed to my lungs, although the tumor is still in my testicles. I have shortness of breath and occasional chest aches. This has gone too far; I need to tell them, as I am scared for the stability of my own life.

Reddit, how do I go about informing them of this? I almost can't bring myself to do it, and I'm truly alone and scared other than the support of my long-distance girlfriend.

Edit: For those of you wondering if I've seen a doctor: no. For those of you saying I'm only assuming it's a tumor and I'm wrong. I'm 100% certain. I have white dots all over my testicles. the area where the tumor is is fairly pale. Please, I know this is a tumor. I just need help.

Edit #2: The right testicle is severely larger.

Edit #3: Well since the kind folks of Reddit have been quick to deny that I have testicular cancer, when it is obvious something is wrong, I will get it checked out tomorrow and come back with an update. Thanks to those who comforted me, though. I'm not just a teenager overreacting to a large testicle. This has gotten serious.

Story Edit: I worded some of this situation badly. I already assumed it was testicular cancer before I heard my mom's story. That only struck me as coincidental.