Fenbendazole, aka "Panacur" (available on Amazon), also SafeGuard. Mycancerstory.rocks excerpt:

Two days after coming home from being told I've got 0% chance to survive, I read a post on the OSU sports board that simply said "If you have cancer or know someone who does, give me a shout" I had known the author of that post (and his sons) for a very long time, so I picked up the phone and called him. He is a large animal veterinarian in Western Oklahoma. What he told me next should have stunned me, but I was fairly numb and not stun-able (new word that should be a word). He told me a story of a scientist at Merck Animal Health (veterinary side of Merck) that had performed cancer research on mice by injecting different types of cancers into different mice body parts. And this scientist stumbled (trial and error) across a product in their canine product line that was batting 1.000 in killing these different cancers. He told me that the scientist in question got diagnosed with 4th stage brain cancer and was told "no hope, 3 months to live". This person decided "what the heck" and started taking the canine medicine. Six weeks later, she was all clear. I had just been told I've got no hope and 3 months to live, so it wasn't a hard decision for me to take the leap.

Sorry about your pups. Most vets are unaware of this research. Big Pharma can't be having cancer cures, now can they?