I suggest adding plenty of good quality colloidal silver to your dog's water. It works wonders in general for older dogs, as many here in CZ can attest to and dogs seem to instinctively know that it is good for them. In fact, I have been told more than once that if you put water containing colloidal silver next to plain water, a dog will go for the colloidal silver enhanced water everytime. How much to add? Plenty - there is no risk of over doing it and I promise that you will not end up with a "blue dog".
Here locally, Inositol/IP6 has been used with great success on animals and humans to get rid of tumors, including eliminateng a baseball sized tumor from the neck of a mule in only a couple of weeks.
I might add that I have a first hand eye and ear witness report who heard Dr. H. Z. Ozel in Turkey relate that he discovered the oleander extract the he later came to patent as Anvirzel (you can make it at home for pennies) while searching for a cure for his family dog's cancer tumors.
Oleander has had success in animals (but you do have to carefully boil and strain it according to directions - raw oleander is extremely toxic), and it has had very good success indeed against liver cancer. The person who devised the homemade "oleander soup" patterned after Ozel's original pattern first used it to rid his elderly mother of liver and stomach cancer.
If you should decide to try the oleander, unlike colloidal silver start very, very small. Perhaps 1/8 to 1/4 teaspoon a couple of times daily and work your way up to the equivalent of 1 tablespoon three times a day for a 180 pound adult (by which I mean divide your dog's weight by 180 and reduce the oleander extract accordingly).