Scientists have adapted an engineered human blood opsonin protein known as FcMBL, which was originally developed as a broad-spectrum pathogen capture agent, to target circulating tumor cells — the notoriously rare and difficult-to-locate agents of metastasis. Using magnetic beads coated with FcMBL, they were able to capture >90 percent of seven different types of cancer cells, demonstrating that the approach could be valuable in cancer diagnostics and monitoring.