FILE - In this June 3, 2010, file photo, Dr. Steven Birnbaum works with a patient in a CT scanner at Southern New Hampshire Medical Center in Nashua, N.H. A national study suggests the world's top cancer killer isn't always as deadly as doctors once thought, finding that more than 18 percent of lung cancers detected in screening scans are likely so slow growing that they’d never cause problems. But the provocative results are unlikely to change how doctors treat lung cancer. (AP Photo/Jim Cole, File)