Look up Cole's Cancer Killing Concoction (if you can still find anything about it online.)

tl;dr, clear back in the 1800s a doctor studied a patient who made a miraculous recovery from facial cancer. What he found was that there are bacteria that cause infection in weakened cancer cells more easily than in healthy cells. So he devised a treatment where a patient with cancer would have a live bacteria culture injected directly into the tumor. The cancer cells would get infected quickly, and "lure" the body's immune system to those cells to destroy them. He cured lots of patients using this technique.

But guess what happened? It couldn't be patented. When Dr. Cole died the entire this was disappeared from the medical industry.