(CNN) - Herman Cain took some hits in Tuesday's CNN Republican presidential debate, but so far the biggest opponent he has ever faced appears to be cancer – a battle he says he has won. In 2006, the former Godfather's Pizza CEO says, he was given a 30% chance of survival against his stage 4 colon cancer.

It started when Cain experienced discomfort in his lower belly, according to a letter written earlier this year by one of his physicians, Dr. Martin York of Peachtree Hematology-Oncology Consultants in Atlanta.