Blood-based multicancer detection (MCD) technologies have been touted as a revolution in early-stage population screening and testing for a wide range of cancers. MCDs (often called liquid biopsies) look for fragments of DNA and other biomarkers in the blood, which may indicate the presence of cancer and predict where it originated. The seductive premise has been clear: detecting cancer earlier and intervening at an earlier stage will cure more patients. Given this promise, the commercial market has grown to more than 24 companies, and the annual global market for these MCD technologies is estimated to reach US $2.9 billion by 2030.