I'd like to add my last Dog had issues with tumors all his life. Can't prove it but I believe it was due to the food. That dog was special. He was a mutt of the highest degree,Rottie/Pit Bull and German Shorthair Pointer.
Climbed trees,ran deer down and had a real problem with ground hogs. He'd hunt them down,find where they lived and wait until they emerged and pounce on them from 10 feet way. grab 'em by the head and 2-3 shakes and they'd had it. Then it was dinner time. Pretty gruesome sight. One time I came home and he was in the yard playing with one of the kills. Threw it up in the air,he heard me coming and looked at me. The carcass landed on his head like a Dan'l Boone hat. He just sat there panting waiting for me to make it down the driveway.
Anyway I spent thousands throughout his life on surgeries to remove tumors. The last time the Vet buffaloed me into a big surgery at 12 years old. The biopsy came back malignant but he said it was a slow growing type of cancer and should it return he'd be done by them anyway. 4 months later he stopped eating. X-rays showed him riddled with tumors. I was told to take him home feed him well and he'd tell me when it was time. He did. As I sat there with him while they administered the drugs he looked up and gave me a big slurp on the face. 10 seconds later he was gone.
Feed your dog the best you can afford. He'd do the same for you.