If the vet hasn't already brought it up, ask about palliative vs "curative" (I think that's what it's called) treatment.
Palliative chemo is designed to stall the cancer or reduce the symptoms, but isn't nearly so intense as a treatment that attempts a cure. We opted for palliative treatment for a Brittany in her last year with breast cancer. I don't remember the exact details. I think there was initial surgery possibly followed by radiation. When the cancer returned after a year or so, we went with palliative chemo. The chemo (a single treatment, every few weeks) would cause her to lose her appetitie and have some vomiting for a couple of days, then she would feel pretty good for awhile. She was nearly 14 yrs old when the chemo stopped having any good effects, and we let her go. We gave her 5 palliative treatments over a span of many months, and I think we should have quit at 3, definitely 4.
"Cancer" covers a lot of territory and lymphoma is not the same as breast cancer. You'd need to talk to an oncologist about what the options are.
Good luck and I'm sorry. The main thing is to enjoy the time he has left, whatever option you choose.
