University of California - San Francisco Jun 12 2026 Cancer drugs can shrink fast-growing tumors. But sometimes a few tumor cells survive. These "persister" cells seed new tumors, forcing cancer patients into arduous cycles of testing and treatment.  The problem is, persister cells are rare - as few as one in a thousand tumor cells - and they're genetically identical to the tumor, which makes them hard to find. Plus, their tenacity can be temporary, and by the time a scientist can get them in a