For breast cancer survivors, the finished treatment brings both relief and a new kind of anxiety. Their scans show no sign of disease, yet the doctors know there’s still a chance the cancer could return years or decades later. The reason is dormant tumor cells, which are tiny clusters of cancer cells that survive treatment by going into a “sleep” mode. These so-called ‘sleeper cells’ are not visible on scans and do not cause symptoms. However, they can hide quietly in bone ma