See a rodent vet as soon as possible. http://www.rmca.org/Vets/ has a list of good rodent vets. The mulp can be a tumor or an abcess or something else, but only a vet can tell you what exactly and how to treat it.
You should definitely take it to the vet to check that out, hamster are very prone to cancer.
because he is a lump
It is proabably a sore. Does it live with other hamsters? If not, you should definentally get it checked.
There are no home remedies for tumors, you should get your hamster checked by a vet.
it wqill have a lump on its butt
If it does not get better in a week or so then go to the doctor and have it checked out.
The Hampster needs expert medical treatment so you should take it to a vet.
Look at their belly. If there is a black lump there, that is the male reproductive system, meaning the donkey is male. If there is no black lump, the donkey is a female.
belive me after a whil you will know the male will have huge balls that looks like a butt under its tail. and the female will not have this. the female will eventually have little nipples that the male will not have.
The chest in front and the rump in the back.
A tumor on a hamster can appear as a visible lump or swelling on the body. The tumor may vary in size and shape, and it can be either firm or soft to the touch. A vet should examine any abnormal growth on a hamster to determine if it is a tumor and assess appropriate treatment options.
Unfortunatley, cancer. Hamsters can get things stuck in their food pouches, which is still bad.