No doctor or immunologist would ever claim that a vaccine (or any medical treatment) is wholly without risk. It's just that the risk of vaccine injury, or in your sad case, vaccine induced sarcoma, is vastly outweighed by the risk of the disease that is being vaccinated against.

At-least its better than someone dying a horrific and gruesome death.

I'm so sorry for you and your cat :(.

Yeah it happens, our dog is battling immune mediated thrombocytopenia right now that they think is related to the leishmaniasis booster he had. It's rare, but the irony is that it would have been much easier to treat the leishmaniasis and he might not be near death in the ICU. Rabies and parvo are much more dangerous and harder to treat though so you have to risk it with the vaccine because the alternative is worse.

I unfortunately had a cat pass away from a vaccination. Off the top of my head, I can't remember which one. He just had a bad reaction to it and was gone the next day. I've grown up with many cats and that was the only one that ever had a bad reaction. Even after that happened, all cats I had after him still went straight to the vet and got all their vaccinations.

It was so immensely sad, but it didn't prevent me from continuing to vaccinate my animals.