Bladder Cancer :(

My 11 year old dog has just recently been diagnosed with bladder cancer (carcinoma). Thankfully the growth (small) is not around when the urine empties but is on the other side. Vet said that is a good thing as it will not obstruct the flow of the urine. She is putting him on Piroxicam and would like to see him back in a month for a check up. He is on Clavamox now as she thought it might be a bladder infection and indicated that he should finish that medication. I am pretty stressed out over this especially due to not knowing what to expect. He is a 11 years old and behaving normally except for occasional incontinence and some blood in his urine. He's had a history of bladder stones so we had initially thought these symptoms were from stones. The vet is feeling somewhat optimistic and we are both hoping the Piroxicam will do the job. Can anyone shed light on this issue but please no bad news. So stressed and upset right now! Any diet changes I should put him on or any helpful advice please!