John B. Kisiel, M.D., a gastroenterologist at Mayo Clinic's campus in Rochester, Minnesota, discusses a study that identified the source of cancer in patients' gastrointestinal tracts by analyzing DNA markers from tumors. The results open the possibility that doctors may one day be able to screen for cancer anywhere in the body with a noninvasive blood test or stool sample. Research findings were presented in a poster presentation at the American Association for Cancer Research 2015 annual meeting.