While I do believe conspiracies happen even in the free world (I love the Warren commission's reasoning for why Jack Ruby killed Lee Harvey Oswald), they are usually just THEORIES.
I have heard the "stories" of the 100 mpg production car engine, but it is still just a story.
Web search cancer cure conspiracy, and there is wild discussion...of course more emotionally charged than the super engine discussions, because we are talking about life and death.
On a less dramatic scale, there are obviously conspiracies everyday involving insiders trying to hide something for personal gain. But when it comes to a cancer cure, there is too much money and potential infamy at stake for everyone involved to hide it. The only credible reason I can see for a lasting coverup would be if a no-return cure was discovered -- like eating a readily available herb or perhaps a slightly better drug was on the cusp of approval, but corrupt individuals could discredit it through selective statistical analysis to keep the standard drug (from which they or connections gain). The numbers posted for recaf are too big an improvement over standard tests to cover it up for long.
The ESSIAC story is an interesting one, and on itial reading by a terminally ill person might give some hope of cure and/or anger toward establishment holdups. The product is still out there, but the allopathic (conventional) medical community really hasn't given it much notice for years.
Fortunately, most corrupt people run in packs, and eventually they double cross each other.