Even if there was a "cure" to cancer, it would never be revealed. The government and big executive leaders make too much money off of patient's spending loads of money on treatment etcetera. Also, consider this, in Australia we have free basic healthcare, and the government will help fund your cancer treatment, if you go by treatment, the unnatural way. But they won't help if you want to treat yourself by taking a more natural pathway, because they know it helps dramatically. For that reason, less people go the natural way and go with the time devouring and not-so-cost-effective mainstream way, which also means you can't tell anyone about it, they have to come looking.
So, in short, we can't cure all cancers, but we can defeat some, the government knows this, and still tries to prevent it without looking to suspicious, by starting up charities etc.