Have you looked at cancer starving diets and immune system supplements? We have unfortunately lost several dogs over the years to cancer and found that these helped a lot.
Janni, my second rottweiler and heart dog (Chrome's mother and Elfi's grandmother), had osteosarcoma of the jaw towards the end - she was 12 when it was dx'd and 13 when she passed away. She had already had several mastectomies for metastatic breast tumors and had been on a cancer starving diet since she was about seven. We also used Lew Olsen's supplement,
Berte's Blend.
Her tumor didn't bleed a lot, it was the smell that got to us, but it didn't bother her, so we just learned to live with it
Liz