Have you talked to a veterinary oncologist? They might be able to give you more information on treatment options or at least give you some information on treatments you read about on the net
I hope you find something to help Harry and he's better soon!
"We are--each of us--dying; it's how we live in the meantime that makes the difference."
"It's not what you gather, but what you scatter that tells what kind of life you have lived!"
"Be kinder than necessary, for everyone you meet is fighting some kind of battle."