Testing for a biomarker in lung cancer patients’ blood could indicate whether they have brain metastases (cancer spread to the brain). S100B, a protein found in the brain, is usually kept separate from the rest of the body by the so-called blood-brain barrier (BBB). Brain metastases weaken the BBB, allowing S100B to enter the bloodstream. In a recent study, researchers were able to identify 89% of patients with brain metastases by measuring the S100B blood levels of lung cancer patients, although the test also produced a number of false alarms. A blood test for brain metastases would likely be much cheaper than the brain scans currently used.