BioKeys. The Crucible (en Inglés) - Troy Aikins

Survival isn't the goal. It's the price of entry.
Stellan didn't come looking for a fight.
He came to fix what was breaking inside him.
Instead, he woke up in a cage.
Sold into The Crucible-an underground arena where enhanced fighters are thrown into engineered death matches for profit-he's given a number, not a choice. Fight. Win. Or disappear.
But Stellan isn't like the others.

Something in him doesn't follow the rules.
His biokey isn't stable. It isn't controlled.
And the more he fights, the more it changes.
Watched by gamblers. Studied by handlers.
Surrounded by killers who've already accepted the system-Stellan refuses to.
Because there's only one rule he cares about:
He's getting out.
Even if it means breaking everything the Crucible was built to contain.