Absolutely it doesn't, but a proof of concept is still an extremely useful thing. A proof of concept means that the thing did actually work once, for one person. Which is far more than all those in vitro studies where sprinkling shavings of gold in the test tube killed the cancer, or whatever.
Sure, there are a few possibilities in which this case would have shown nothing at all
- The woman's cancer went into remission suddenly and for unrelated reasons a day after the intervention (seems highly unlikely)
- This woman is one of the only people in the world for which this treatment would work (seems highly unlikely)
- Something else caused the remission (mercury and formaldehyde in the vax..?)
- The authors are being misleading, deliberately or not (certainly possible)
You're absolutely right to say that one should be cautious about anticipating a miracle cure for cancer. But, that said, there's a good reason that this one case of it working on one person has made the news: much like the girl who was cured of AIDS, it very likely means something.