MC transformation, bloodlust, revenge

Looking for books where the MC (through immense torture, genetic experiments, or other body-altering events) changes drastically, and comes out the other side a seething, manic monster hellbent on revenge. The MC becomes the horror themselves almost. I want violent wrath and punishment enacted upon the perpetrators, that kind of thing. I request that we keep it suuuper fictional, preferably with sci-fi elements or body horror.

Edit: Halfway through Exoskeleton by Shane Stadler. Kind of the vibe I'm going for here.