A virus gotten from the outside world is a bit different than a mutation of the bodies cells, as in cancer.
Btw, massive vit. C does indeed kill the flu and cold virus. Doctors used to use it a lot in the old days.
Modern science has shown an irrefutable link between some viruses and some cancers.
As for what doctors did in old days, based upon things that happened in vitro, they believed in mercury cures too.