New Hamster - Worried it is sick

Question
I just bought a dwarf hamster from the pet store, and my roommate made a comment about it having an enlarge butt area.  She had said that she had a hamster die from having this, but she does not know what kind of sickness it is.  The hamsters are very small and I got them from a local pet store, so I'm assuming they are young.  I just wanted to find out if this new addition might pass prematurely.  A quick response would be greatly appreciated. Thank you!

Answer
Do you know if its a boy or girl? If it's a boy then it's more than likely his testicles. Is the hamster eating and drinking as normal? If so then it's probably his testicles, hamsters do have large testicles. If h's not eating and drinking normally then I would seriously take him to a vet to get looked. When a hamsters bottom swells it's a good indication of having intestinal problems. Generally when a hamster has wettail their stomach or bottom gets bigger. Dwarf hamsters however don't get wettail. They can get diarrhea but the bacteria that causes wettail doesn't happen in dwarf hamsters.