Oh, I am so sorry for the diagnosis.
Two of my older dogs were diagnosed with cancer.
Louie, my Lab, had a tumor in his paw. At first I opted for the mass to be removed, but the Vet couldn't get a clear margin. So, then he removed the digit. Unfortunately the cancer had spread. My holistic Vet put him on herbs to strengthen his liver function. Other than that, I watched for signs of pain. Lou continued running like a puppy a little longer.
Carlos Garcia, Lab/Chow was diagnosed a few days after I let Louie pass over. His neck lymph nodes were the size of plums. I did not opt for chemo, as Carlos was about 12, found as a stray on our street 5 years earlier. For him, I managed his cancer with prednisone. There is a theory that it slows it down. His appetite was tremendous and I made him beef stews or chicken soups. Lots of vegetables and brown rice. I do not feed raw. And I actually COOK for my sick dogs.
I am glad you are there for your friend, and I know it is very difficult. If you want to pm me for emotional support, I am good listener.