KingD19
Shai-Gen's Enigmatic Wong
I already pointed it out. But I'll do it again.
The proof is that he was molecularly fused with a large amount of concrete due to Shadowcat phasing him into the ground. The proof that things she phases are fused with whatever they're being phased through if she lets go of them is in X2 when a girl who is clearly Shadowcat phases through the floor in the mansion and her blanket is stuck in the ceiling because she didn't take it with her. Also that's just how her powers work.
After she phased him, he was completely unharmed when he broke out. So either he is A)So durable that he can completely ignore having his molecules fused with foreign substances that should for all intents and purposes be janked up in his body.
Or B)He just heals so fast that the moment he broke out, he healed. In the deleted scenes Wolverine stabbed him in the arm. There wasn't even any blood, and Cain didn't seem to register any pain. And as soon as the claws were out of his arm, there was no damage.
So it seems to be one or the other. Hell maybe it's both. Also as mentioned he doesn't even seem to register pain so he'd more than likely keep fighting even if the daggers did any damage.