GBM (IMAGE) University of Pennsylvania School of Medicine Caption A blood test that measures the amount of cell-free DNA (cfDNA) in the bloodstream -- called a liquid biopsy -- correlates with how patients will progress after they are diagnosed with glioblastoma. Credit Penn Medicine Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.