KRAS and colonic neoplasm: Although exogenous expression of mutationally activated K-Ras alleles has been shown in other studies to favor expansion of the CSLC population in colon cancer models [51, 52], to our knowledge, this is the first study to demonstrate the essential role of endogenously expressed K-Ras in the maintenance of the self-renewal and tumor-initiating capacity of CSCs/CSLCs.