Lots of training.
Even if you have good genetics, you still need lots of training, and you need to have started early in your lifetime with that kind of training. Even if you don't have the genetics, with lots of training (training very smart, of course), you can still mold your body into a professional athlete, provided that you start early enough.
Desire too is critical- if you don't want it, how can you go for it?
Dedication- for that kind of training, you really need to be dedicated. I mean, all you're doing is training day in and day out for years and years.
Money- because if you aren't supported, you can't train as much, and you won't be able to progress. That includes money for getting tested, money for high performance gear, money for travel, money for coaches, and money for travel. And I'm not even talking about living expenses, which is a whole different ballgame.
Support- support from family and friends, a support team of coaches and other peers in your sport, support from sponsors and bike shops, support from your job and/or school (if you're still a teen), and medical support.
This is probably just a start for things you would need to race at that level.
Koffee