I find it funny that you say cancer is not a behavior, when you can find plenty of cancers caused by behavior (smoking, too much sun, etc), but you will rail on about mental being by the devil.

If the devil is at work, why wouldn't/couldn't physical disaease be the result just as easily as medical? Maybe doctors just explain it now better than they did before.

You see the hypocrisy there?

How about this, both are or can be purely genetic. I'm sure people died of cancer in the olden times, but science has gotten better and able to determine that now, just like they have with mental illness. And if Satan can attack though the mind, he can also attack through the body.