Cancer is a series of genetic or epigenetic malfunctions. It's not a spiritual or emotional disorder. You don't get cancer because you're a bad person, or because you've built up too much karmic debt, or because you slept with your best friend's aunt's room mate's boa constrictor. And stress may certainly be a factor in lowering immune response and aiding in the progression of disease, but negative thoughts alone, launched out into the cosmos, are not going to be flung back to you a hundredfold by an advanced race of ancient aliens with a bizarrely vindictive agenda. I almost promise. Besides, they're too busy experimenting on my reproductive organs as I type this. Did I say organs? Plural? Yes, I've been enhanced. By aliens.
There is also no cure for cancer. This is terrifying, and a lot of folks can't handle information like that, even if they've never experienced the disease personally. Death anxiety inspires a lot of funky behavior, including the urge to make shit up for no reason, as well as the urge to be taken in by said made up shit.