Serious answers only about hampster's imminant demise?

I have a hampster. About six months ago, I noticed a "growth" down by where he goes to the bathroom. Friends who had owned these type of critters told me it was the testicles. I didn't think so. Anyway, during that time, the thing has grown and grown. I have watched this thing go downhill by appearance ever since. He has scabs on his head and legs, this growth is about the size of large marble or the cirfrance of a quarter. He is losing his hair and due to the growth, is moving very slow. I took the position early on that I was not going to treat whatever was wrong - if I even could - I also took the position that as long as he was eating and drinking and excreting waste normally, I wouldn't "do" anything. Well, I fear I may be getting to a fork in the road here soon. Where I have to make a decision. My question - do Vets ever put to sleep an animal of this size or what other humane thing could I do - or should I just let nature take it's natural course?