Here is an article about a possible cure for cancer, which already exists in the form of an inexpensive chemical, which makes it difficult because no one will put up the money to get by FDA approval.  Here is an excerpt, you can link to the article here.

By Bill Walker:
The good news this month is that a Canadian team under Dr. Michelakis at the University of Ottawa has discovered that a simple, inexpensive chemical is a powerful anticancer agent, effective against a broad range of cancers. (Read their paper in the January Cancer Cell, subscription required). The bad news is that it is a simple, inexpensive chemical long used in medicine, and is not patentable. Thus there is no mechanism for getting the chemical (dichloroacetate, DCA) past the billion-dollar barrier of FDA approval. (The FDA actually only approved 17 drugs last year, and the drug industry spent 40 billion dollars on R&D).