Low-dose computed tomography (CT) scans are the currently recommended screening method for lung cancer in heavy smokers. However, these scans produce many false positives (identifying suspicious lung nodules when no cancer is actually present), needlessly exposing numerous people to the costs and risks of invasive follow-up procedures. Now, a large study has shown that a simple blood test may complement CT scans to reduce the false positive rate in lung cancer screening. The microRNA signature classifier (MSC) Lung Cancer assay measures the expression levels of several molecules called microRNAs to classify patients as low, intermediate, and high risk. In a trial of over 4,000 current or former smokers, the MSC Lung Cancer assay detected the vast majority of all lung cancers accurately, but produced a low rate of false positives. Moreover, the test detected some cancers up to 2 years before the CT scans.