It is not only possible, but very probable that Lance Armstrong, at some point in his career, knowingly took performance enhancing drugs that had nothing to do with his cancer treatment.
The thing is, Lance isn't alone. As a matter of fact, he's just like many other professional endurance athletes, especially in the cycling world.
He's an amazing athlete and an amazing human being and I won't take anythig away from him...yet. But you just have to realize how prevelant doping is in professional sports.
Think about it this way: if the guys Lance is beating are use performance enhancing drugs or other forms of doping, what does say about him? That means he's not only better than all the non-doped guys but all the doped guys too. I don't buy it for one fucking second.