I would suggest that you read through this thread.
http://www.dogforums.com/13-dog-heal...uin-100mg.html (Antibiotic - Zeniquin 100mg)
It's title is misleading because they hadn't diagnosed the dog yet, but it is all about Lymphoma. It is sad, but the story isn't finished yet, and is probably worse than your dog anyway.
Any advice I would have for you, would be in that thread already.
Good luck, and please let us know what happens.