With a family history of colon cancer, Brian Folloder has been getting regular colonoscopies since he turned 35. But in 2009, when he was 62 years old, a screening blood test for medical insurance showed a possible sign of cancer. So, Brian had a CT scan.

It showed no evidence of cancer. Yet, Brian’s son Justin, a physician assistant in Surgical Oncology at MD Anderson, insisted Brian get a six-month follow-up scan at MD Anderson...