PROM1 and colorectal neoplasm: As expected, the cells in the spheres were positive for CD133, but negative for differentiated markers of colorectal tumors, i.e. nuclear β-catenin (activated β-catenin), cytokeratin 20 (CK20) and the caudal type homeobox transcription factor 2 (CDX2) (Figure 2B and 2C), indicating these spheres were undifferentiated spheres.