IMO this belief is incorrect. It is true that pharma won't go after drugs they can't patent, but this is to ensure a return on their investment. We now live in a world where it can cost up to $500 million to just get approval for one drug. No profit equals bankruptcy.
That being said it is completely short sighted to think that Pharma makes its money off of cancer treatment and therefore would suppress "cures". A "cure" for cancer is typically only for one type of cancer and is not a lifetime cure. You can always get another cancer later on that you have to spend money on. Pharma makes FAR more money on living patients than dead. A living person gets heart disease, diabetes, cancers, colds, flus, infections, erectile dysfunction, etc. A dead person does not.