The pathway plays a central role in the development and homeostasis of the gut tissue[9]. The Hedgehog pathway is deregulated in gastrointestinal cancers[42]. Up to 60% of HCC samples express Sonic, the predominant ligand of the hedgehog pathway[42]. Additionally, genes involved in the hedgehog pathway are highly expressed in CD133+ liver cancer SC[43]. It is worth noting that suppression of Hedgehog PLK1 activation pathway decreased HCC cell proliferation and sensitized HCC cells to treatment with 5-fluorouracil[44]. Hedgehog signaling has been shown to be essential for proliferation and

survival of human colon cancers[45]. It is thought to affect both tumor growth and CD133+ CSC[45]. Similarly, HH signaling has been associated with pancreas cancer invasion and metastasis. Conversely inhibition of HH signaling inhibited pancreatic metastatic spread[46]. PTEN pathway PTEN is a phosphatase that antagonizes PI3 kinase activity[47]. PTEN helps control the proliferative rate and the number of intestinal stem cells and its loss is associated with

an increase in intestinal SC[47]. It is also thought that PTEN pathway controls SC activation via interaction with the Wnt pathway[48]. It is also proposed that PTEN pathway interacts with the TGF-β pathway described above[48]. Mutations in PTEN, result in a cancer syndrome (Cowden’s syndrome) characterized by hamartomas in the gastrointestinal tract, central nervous system and skin in addition to tumors in the breast and thyroid gland[49]. PTEN deficient mice exhibit increase in intestinal SC which results in excess crypt formation[47]. Identification of CSCs Eradication of CSC stems is an intriguing concept that provides hope in the possibility of finding a cure for cancer. Any therapeutic modality that targets CSC will require accurate identification and characterization of the CSC and differentiating them from normal SC. Isolation of cancer cells through the identification of pathognomonic

surface markers has recently gained popularity and is an area of active investigation[50,51]. CD133+ emerged Brefeldin_A as a promising surface marker for CSC[50]. Singh et al[51] used flow cytometry to successfully isolate CD133+ CSC in human brain tumors and implanted them into forebrain of immunodeficient mice. Transplantation of as few as 100 cells produced tumors that were phenotypically similar to original tumors. Similar findings were reported in colorectal cancer. Several groups isolated subpopulations of cells, accounting for approximately 1% of total number of cells within a tumor, that were CD133+ and we capable initiating cancer when transplanted in immunodeficient mice[5,52,53]. Other studies have identified new CSC markers (Table ​(Table1)1) that may be promising in isolation of CSC such as Lgr5, CD44, CD24 and epithelial specific antigen[54-57].