I'm sorry you and your hubby are going through this. 💚
I'm hearing more and more these days it seems, about rare cancers. I lost a brother to one 4 years ago. The type was so rare, only about 12 other cases had been diagnosed in the world before him. So few cases, that there was no history on any treatment that might be helpful. They still tried some chemo anyway, just on the chance. One of the biggest ironies to me was that the chemo was supposed to try to fight the cancer, but it also destroyed the body's natural immune system too, which meant that the chemo wasn't fighting it and at the same time, neither could his body fight it anymore. I couldn't wrap my mind around that exactly and sometimes wondered if he would have lived longer without the chemo. There is no answer to that question though.
So... .I believe doing everything by diet and exercise and anything else good for his body is certainly the great way to address it. I do hope you find something that works.
Never give up hope ! Many people DO recover !
It's true that doctors don't know the outcome.