That's how it works in the best case. Unfortunately, medical research is not a perfect science. Realistically, with many medical treatments, you can't have a do

That's how it works in the best case. Unfortunately, medical research is not a perfect science. Realistically, with many medical treatments, you can't have a double-blinded study. With chemotherapy, the side effects will often quickly tell you what treatment you're receiving, and a treatment like for example extracorporeal photopheresis can't ethically be placebo-controlled or double-blinded at all. What are you going to do, hook half your patients up to a machine that will do nothing but run their blood around a bunch of tubes for hours for no reason? And you can't get a "large sample size" of patients with rare cancers or diseases by definition. Sometimes, the best you can do is a case study of ten patients who agreed to try your treatment because the other option was death. Quite a few medical advances have been made that way, actually.