Yes. The Force is like an external energy source flowing through their bodies all the time, amping them in all manners, and the most basic, inherent aspect of "strength" of any basic biological system is the tissue's ability to replace itself properly, and then to defend against various diseases. So basically the cancerous influence would have to surpass the Force's constant aid and fight it.
Any external disease is first forced to go through the Force flow of the person, it's the natural, inherent part of their organisms.
But while cancerous influence and bacteria work temporarily and eventually die, Force flows through those people constantly, and is a constant aid.
Other than deliberately being poisoned, they are basically immune to natural diseases and cancer basically can't touch them, of course relative to their Force connection. The exception is Vong poison, Vong bacteria; Force can aid their bodies in surviving the sickness, but can't aid their defense from contracting the disease in the first place.