What causes early-onset colon cancer? New research offers clues

Getty Images; Tyler Le/BI

Five years ago, Tim Cannon, a cancer doctor in Virginia, saw that his colon cancer patients were getting younger and their cancer was more aggressive. He had just diagnosed three people in their 30s with late-stage colon cancer. More perplexing, all three were athletes who competed in long-distance, endurance sports.

"Within a six-month period, I saw three extreme athletes in their 30s with metastatic, very advanced, incurable colon cancer," Cannon told Business Insider.