PROM1 and colorectal cancer: Metastatic variants of CSCs was initially observed in pancreatic cancer and a CD133+/CXCR4+ subset of CSCs were shown to be essential for liver metastasis.30 Subsequently, CD26+ metastatic CSCs were reported in colorectal cancer.31 An additional study also showed that CD110+ and CDCP1+ CSCs of colorectal cancer led to liver and lung metastasis, respectively.32 However, metastatic CSCs were not identified in other types of cancers, posing the question whether the existence of metastatic CSCs is cancer type-specific.