My Hamster has a lump?

I have a pet hamster. Today I noticed he has a rather large lump on his neck, under his chin (he looks like a bull frog right now). It's about the size of a skittle, maybe larger. If you palpate the area, the lump will roll around. I know hamsters have cheek pouches, but this is more like in his throat. Touching the effected area does not seem to hurt him. I am still concerned. What could it be?