Well, you have to keep in mind that hamsters don't have an enormously long life span to begin with, and many people find tumors on their hamsters when they're 2 years + -- so they ay have only lived a few more months anyway.
I wouldn't be all doom and gloom -- we've had hamsters in our rescue that got tumors removed and went on to live normal and healthy lives. It depends a lot on what type of tumor it is, how big it is and if it's spread, and how skilled a surgeon your vet is. :0
We are as gods to the beasts of the fields. We order the time o' their birth and the time o' their death. Between times, we ha' a duty. - Terry Pratchett.
"Men have forgotten this truth", said the fox, "But you must not forget it. You become responsible, forever, for what you have tamed. - Antoine de Saint-Exupéry