Blood samples taken from people more than three years before a diagnosis show tumor traces Cancer cells, like these dividing breast cancer cells, can shed DNA fragments into the bloodstream. Tests to spot these fragments could aid early cancer detection efforts. Wei Qian/Univ of Pittsburgh, NCI Cancer’s genetic fingerprints may lurk in people’s blood long before they find out about the disease. It’s possible to spot tumor DNA more than three years before a person is diagnosed with cancer, resear...