11/01/2025
Breast cancer often hides in plain sight. Even after successful treatment, up to 30 percent of patients see their tumors return, contributing to hundreds of thousands of deaths each year. A promising new study from the University of Pennsylvania suggests we may have a way to stop this: by actively going after dormant tumor cells (DTCs) that linger quietly in the bone marrow and other parts of the body.
Instead of waiting and monitoring for recurrence, researchers tested drugs that target these sleeper cells directly. In a trial of 51 breast cancer survivors confirmed to have DTCs, hydroxychloroquine and everolimus—either individually or together—proved highly effective. When combined, the drugs eliminated 87 percent of DTCs, and all participants remained cancer-free for three years. Even using either drug alone kept survival rates above 90 percent. Mouse studies conducted beforehand showed similar results and helped reveal why these dormant cells respond differently from actively growing tumors.
These findings highlight that dormant tumor cells are biologically distinct from active cancer, meaning some drugs ineffective against growing tumors can selectively wipe out the sleepers. Not every survivor has DTCs, but for those who do, this approach could dramatically reduce relapse risk. Researchers now aim to expand trials, test different drug combinations, and refine dosing to maximize protection. For many survivors, targeting these hidden cells may finally ease the lingering fear of cancer returning.
Research Paper 📄
DOI: 10.1038/s41591-025-03877-3
