Bad reaction to Piroxicam in dogs

My 8 1/2 year old Rottweiler has just started with major bladder issues. The Ultrasound is showing some type of mass in his bladder. He can't control is urine at all at this point and I am really going crazy. The vet has done a biopsy of tissues via a catheter and ultrasound removal, so no surgery. The results so far are not showing cancer but my vet is having a re-test done because he feels it is. Anyway, my dog is almost 150 lbs so as you can imagine, constant major bladder leakage is really hell currently. If it is cancer, we won't keep him suffering but we are waiting for a definite positive test. Were your dogs as bad with the major straining and constant urine leakage while sleeping, etc. as mine is or is he in the really late stages? Also, I just got Piroxicam today for him. Will this help him with the leakage as the inflammation hopefully shrinks or just slow the growth if it ends up being cancer? Thanks in advance for your comments!