Tumor, Cancer or other?

[Oatmeal_Cupcake]

Age: 1 year 8 months
Gender: male
Species: Syrian

These are the details of my hamster's ailment -
When did it start: noticed it in September, noticed the size increase last night.



So I just got back from the vet. Surprise! The vet doesn't know what it is. He suggested to either freeze it, which will only address the problem externally if there is any growth underneath. The other option is surgery. One of the concerns would be if he has enough skin to close up his arm. The second concern is the stitches. Since it's on his arm I am worried that he will pick at them and I can't really think of ways to keep him from doing that. The other thing is that he's pretty active in his hospital bin... would he run the risk of opening it back up if he's consistently jumping and trying to get out of the bin?