Number one, get the dog off of "dog food", it will buy him some time, and something to look forward to. I am a believer in Turmeric for shrinking tumors. Keep him cool, low activity, and fenben. He may not get cured but he will live longer, depending on breed, 13 is within the lifespan. My old girl has a brain tumor, and her liver was wonky, I took her off commercial food and she eats chicken or fish with lots of veggies, carrots, lettuce, cooked green beans, canned pumpkin, rice pasta (she needs the carbs because the tumor is also on her pancreas and pumps out too much insulin). I cannot turn back time, but I can make her time here with me comfortable. Turmeric can be added by spoonful to her food, a tablespoon a day.