There were the cures that worked in theory but did not work in actual cells. There were the cures that worked on mice but did not work on humans. There were the cures that cure cancer but have a higher fatality rate than the cancer. Those cases cover just about every cancer "cure" you read about in the news.
Then there are all the cures that work for some people some of the time. Big pharma has patented them and is selling them for enough money to cover all of the other cures that did not work (and give everyone a very nice bonus).
Seriously, if some phara company could cure cancer, why wouldn't they? They can sell it for 100k per treatment, make enough money for each of the 10 biggest investors to buy a small country, and then close up shop.