It’s a long-running medical mystery: Why have so many people under 50 in affluent countries been developing colorectal cancer in recent decades?

Something new is triggering a jump in what’s known as early-onset colon and rectal cancer (EOCRC). The rates have been going up for the last 20 years and no one knows why it’s happening. The usual risk factors for CRC —obesity, smoking, bad diet and lack of exercise— don’t fully explain the increase.