Did not have the same heath condition the dog is doing good just did not know what kind of dry food to give. I hope your dog is doing better.
Actually, the Natural Balance foods are good. I have a Grey that is having protein problems and needed a food low in phosphorus. I switched him to the Natural Balance Fish and Sweet Potato. He was diagnosed in May with Lymphoma. :-( I am still feeding him the Natural Balance Fish and Sweet Potato with a high protein *stew* I cook up plus cottage cheese and about 2000 units of Omega 3 daily. If the tumor is cancer, theory is you want to feed a high quality protein and no or very little carbs. You can also feed Salmon, canned sardines, etc.
You don't really have to cook, per se. You have a crock pot? I just throw everything into a crock pot (mainly lean ground beef, I just brown lightly, chicken breasts, liver, vegetables such as canned green beans, squash, some garlic and some brown rice.) To that I add some low sodium chicken or beef stock and water. I've been adding this to his Natural Balance alone with low fat cottage cheese twice a day.
Actually, there are a couple of Yahoo groups with tons of information, if you are dealing with cancer. There is a canine cancer group and another group that is treating with artemisinin treatment.
Due to my dog's age and pre-existing health issues, I have opted to do palliative care only. You might want to look at those groups.