[header] How to diagnose tumors in hamsters [title] Look for lumps on the belly. [step] Hamsters can develop different types of tumors as they grow older. Lymphoma, which is a cancer of the immune system, is a common tumor in hamsters. 
It can affect many internal organs and lymph nodes, resulting in the formation of lumps in the belly. If the lumps are large enough, you would be to see and feel them.