Everything causes cancer. Being paranoid about cancer causes cancer. Seriously though, while there is little evidence to prove as much, theories suggest that microwaves can have an impact on brain and skin cancer.
No, it doesn't. This fear of getting cancer from the microwave is like, gently poking someone with a toothpick and they fear it will impale them. The rays emitted are so, low powered, and weak, they don't affect you, even if you have your face against the view screen and crank that thing on for an hour, each day, each month, etc; you would more likely get killed by a mosquito infecting you while you stand there, than getting cancer.