The Food and Drug Administration on Monday approved the first screening test for colon cancer that uses patients' DNA to help spot potentially deadly tumors and growths. The Cologuard test from Exact Sciences detects irregular mutations in stool samples that can be an early warning sign of cancer. Patients who test positive for the mutations should undergo a colonoscopy to confirm the results. Doctors have long used stool tests to look for hidden blood that can be a warning sign of tumors and precancerous polyps. But company studies of Cologuard showed that it was more accurate at detecting cancerous tumors and worrisome polyps than traditional stool blood tests.