Cancer is the result of a defective immune system - our bodies produce cancerous or pre-cancerous cells constantly but a healthy immune system is always on the alert and eliminates rogue cells. Anything that supports or strengthens the immune system can't hurt, but considering the expense of some of these supplements, the one credo I came to understand while researching Nikki's lymphosarcoma was that if it sounds too good to be true, it probably is. One of the very few "truisms" that is acknowledged by academia is that cancer cells "feed" on carbs, so feeding a high quality, grain free diet is a generally a good place to start.
I am so sorry that you and Caesar are going down this road together! It is excruciatingly painful. You are in my prayers!