Is he getting healthy fats? Have you heard of the Budwig cancer diet, I guess it’s been adapted for pets, although seems to me like it could cause some diarrhea - I know with humans it’s basically flaxseed oil and cottage cheese, but the amount of oil can be slowly increased. You can Google Budwig cancer diet for pets.
I definitely believe sugar fuels cancer growth - and what do they tell cancer patients who can’t eat? Drink a supplement full of sugar!
He eats only raw chicken (dark meat only because it’s fattier, bones and all), coconut oil, olive oil, occasional other fats and some veggie scraps. There is a study on-line showing a ketogenic diet’s dramatic efficacy against mast cell tumors so we keep at it.