Probiotics such as Forti Flora may be helpful; these products can help boost the immune system. Many pet stores carry them or they are availalbe on the internet.
There are a number of spices shown to have anti-cancer activity.
Garlic --Try FRESH minced garlic - about 1 clove per 40 pounds of body weight. Be careful of the dose, though, since in large amounts, garlic can cause toxicity (anemia). A cbc (complete blood count) should be monitored regularly to monitor potential problems.
Turmeric, the yellow (and rather mild) spice that gives curry its yellow color, is a strong antioxidant. Turmeric is rather milder tasting than one would expect. Most dogs accept it readily. The dose of turmeric is high, up to one tablespoon daily for large dogs. It's best to obtain it as fresh as possible from either an store that sells Indian spices or it can be ordered online at Penzey's (LINK).
Again, I'm sorry that you and Woody will have to going through this but I hope this answer provides you with some options to consider.