Well, most people who catch rubella get better with no treatment beyond bed rest and chicken soup. I’m sure that if you add vitamin C and juice to that regimen, most of them will still get better.
Of course, a few people who catch rubella are seriously injured or die, and everyone who catches rubella can spread it to other people, some of whom may be in the unlucky group.
Very few cancers are contagious. I was sad that Steve Jobs died after he tried to treat himself with juice and vitamins, but hey, his body, his choice.
fwiw, I know several people who have recovered from cancer after conventional treatment, which can include chemo, radiation, surgery, or fancy experimental immunological treatments. And I know others who died.