The amount of money to be made from a cancer cure would be astronomical, I would imagine. Any company sitting on a cure would seem to be forfeiting an ungodly amount of money to keep up a perceived "racket". Then again, maybe they saw I Am Legend and got cold feet.
You're ignoring the hospitals, radiation tech companies, and huge amounts of various pharmaceuticals. It also depends on what the cure would be. If its just a pill or single surgery for instance, it would be minuscule compared to what it costs to treat today. In fact its hard to imagine a cure that would come anywhere near what it costs on as a whole today. And I don't think anyone is saying that anyone is sitting on a cure, I think people are saying that alternative treatments are being both underfunded and unfairly prejudiced by the system. Even if some people are exaggerating that I think its true enough.