An advanced healing factor is something that runs rampant in comics. Numerous heroes and villains heal from injuries in a matter of hours that might kill an ordinary human. That’s not exactly the case for Cable.
Cable has found himself with superb healing when
he and Deadpool have ended up merged due to a teleportation incident. Deadpool stays alive in the most absurd circumstances because of his extremely powerful mutant healing. When their bodies merged while teleporting together, Cable had access to that healing as well. That’s not the kind of healing that Cable has as a superpower though.
Instead, the healing that Cable exhibits is actually aimed at other people. In the series Cable & Deadpool, Cable ended up in another reality and deaged to an infant. When he returned to his own reality, he rapidly aged as his powers manifested quickly and strongly. During that time, Deadpool was actually brainwashed into wanting to take him out, with, as Cable discovered using his telepathy, “black spots” in his brain.
Though the act could burn out all of Cable’s power, he uses his abilities to heal all those black spots in Deadpool’s brain, helping to fix the gaps in his memory and purging illness from his system. Of course, Wade’s mutation and his cancer still seem in tact after the fact, so even Cable’s immense power can’t totally heal him.
It’s unclear just where this healing power comes from. An offshoot of Cable’s telekinesis, perhaps, manipulating the cellular structure in the brain?