Additionally, almost all murine GBM CTCs expressed Olig2, and 40% expressed CD133 [9]; CSC markers are detected on a fraction of CTCs in a variety of types of cancer, including breast cancer (CD44), colorectal cancer (LGR5), non-small cell lung cancer (NSCLC) and ovarian cancer (BMI1, CD133, ALDH1) [10–12]. Here, PROM1 is linked to breast cancer.