Here's an alternate explanation:

Maybe cancer is way to common and keeps being formed in the human body... but also the body gets rid of it by itself. This is why most people who have cancer never find out about it.

The few people who are always going for "regular screenings" are the only ones who find out about it and get "treatment" when it was completely unnecessary.

Here's another alternate explanation:

Maybe what is marketed as "healthy" by the food industry by funding scientific research and selecting results favorable to them is not really healthy.