CD133/prominin-1, a pentaspan transmembrane glycoprotein, has been initially described as a surface antigen specially to human hematopoietic stem cells  and CSCs with CD 133 positivity have been implicated in tumor progress as identified in tumor growth of pancreatic  and colon cancers . AC133, i.e. CD133, polypeptide has a predicted size of 97 kD and contains five-transmembrane (5-TM) domains with an extracellular N-terminus and a cytoplasmic C-terminus. Whereas the expression of tetraspan (4-TM) and 7-TM molecules is well documented on mature and immature hematopoietic cells and leukocytes, this 5-TM type of structure containing two large (255-amino acid [aa] and 290-aa) extracellular loops is unique and does not share sequence homology with any known multi-TM family members . Nowadays, CD133 presentation was found in many solid tumors such as brain tumor [4, 7], prostate , pancreatic , hepatocellular  and colon cancers [5, 6], but the specific role of these CSCs in tumor biology, including metastasis and recurrence, is still uncertain, especially in human GC. Although there are different phenotypes in different kinds of CSCs, the higher expression of CD133 as same phenotypes has been identified in CSCs, especially in solid tumors derived from epithelium cells of gastrointestinal organs [5–7, 12, 17]. O'Brien and his team  identified CD133 positive cells shared the characteristics of human colon cancer-initiating cells, in which CD133 positive cells were able to initiate tumor growth in minor quantity of the cells Moreover, CSCs with CD133 positivity possessed strong carcinogenesis, cloning ability and proliferating capacity as demonstrated in many experiments [4–8, 11, 12, 17], and were resistant to anti-cancer therapy [10, 18]. Hence, the metastasis and recurrence of cancer as one of main factors inflecting on the prognosis has still been hard to be overcome thoroughly until now.
Regulation and control on gene expression is partially dependent on the transcript and the protein expression appearances. As reported , the initiation and the proliferation of colorectal cancer were based on CSCs with CD133 positive only in minor quantity, which was also identified not only in prostate , pancreatic  and hepatocellular  cancers but also in gastric cancer [12, 19]. In this study of ours, CD133 protein positive structures had been seen in 29.3% cases in primary lesion of 99 patients' group, but no CD133 positive structures in NCGT. Simultaneously, CD133 mRNA expression had been identified in all primary lesions of 31 patients' group, but only 16.1% cases in NCGT of this same group. As compared with the level of CD133 mRNA BSV in NCGT, this value was significantly higher in primary lesion. Additionally, CD133 expression significantly correlated with tumor diameter of > 5 cm, later TNM stage and T3-T4 as stratified analysis. Furthermore, either severer invasion depth or later TNM stage was the independent risk factor for CD133 protein expression. Therefore, it can be concluded from the above mentioned results that the tumor cells with CD133 protein and CD133 mRNA may play some important roles in the growth and the invasion of GC in human being.
Hermann PC et al  demonstrated that a subpopulation of migrating CSCs with both CD133 positive and CXCR4 positive was essential for tumor metastasis of pancreatic adenocarcinoma. Mehra N et al  examined whether RNA expressions of CD133 and CD146, a pan-endothelial marker, were increased in the blood of cancer patients and whether these factors correlated with patient characteristics and were predictive factors of survival. Their results in the peripheral blood mononuclear cells of 131 progressive cancer patients, 37 healthy volunteers, and 5 patients who received granulocyte colony-stimulating factor showed that patients with metastatic disease had a significant increase in CD133 mRNA (P = 0.03), specifically patients with bone metastasis (P < 0.001). In a recent study, it had been examined whether increased levels of expression of CD133 mRNA by semi-quantitative real-time RT-PCR analysis in peripheral blood predicted disease recurrence in patients with colon cancer. Their results indicated that elevated CD133 mRNA levels predicted colon cancer recurrence as an independent factor in Stage IV of TNM disease . Similarly, the higher level of CD133 mRNA in primary lesion occurred in subgroup with lymph node metastasis, and this elevated level was positively relevant to the increments of metastatic lymph node ratio or metastatic lymph node number as demonstrated in our results of this study. Additionally, CD133 positive cells in cancerous emboli in vessel-like structures had been observed morphologically as a first report in our knowledge. In the immunohistochemical investigation in this study, CD133 positive percentage in subgroup of lymph node metastasis was significantly higher than that in subgroup without lymph node metastasis. With the increments of tumor invasion depth and TNM stage, CD133 protein positivity rate increased. From such results, it can be concluded that the positive expressions of CD133 mRNA and CD133 protein positively related to the lymphatic metastasis in GC, which can reasonably be considered as a risk factor to lymphatic metastasis and tumor invasion. Hence, the strategies aimed at the CD133 and SDF-1/CXCR4 modulating axis, and the molecular pathway for lymphatic metastasis may have important clinical significances to inhibit metastasis of CSCs.
Ki-67 is a kind of nuclear protein, which expresses in cellular cycle of G1, S, G2 and M phases, but not in G0 phase. In order to probe the relation of CD133 expression with the proliferation of tumor cells with or without CD133 positivity, the CD133 mRNA expressive level was applied in this study due to the rare CSCs (usually around 1%-5% of total tumor cells) with CD133 protein positivity in tumor as common and the difficulty to identify CSCs as immature tumor cells from matured tumor cells morphologically. From current limited information indicated in this investigation of ours, there occurred the significantly higher expression of CD133 mRNA in subgroup with lower Ki-67 LI in comparison with that in subgroup with higher Ki-67 LI. Theoretically, this phenomenon observed in our study could be elucidated as the various biological profiles in different stage of tumor differential process or in proliferating characterization in the early stage of carcinogenesis and tumor development. And this proliferating characterization would be gradually weakened in tumor development probably. Additionally, in some extent, this higher expression of CD133 mRNA in subgroup with lower Ki-67 LI could also be explained to the resistant potential of CSCs to anti-cancerous therapy because tumor cells in Phase G0 such as most of CSCs were difficult to be killed by cytotoxin drugs and radiotherapy . On the other hand, for other explanation of this interesting phenomenon with negative relation between CD133 mRNA and Ki-67 LI, as our consideration, it is also contributed to the different proliferating abilities of matured tumor cells and immature tumor cells of CD133 positivity with some characteristics of CSCs. As well known, CSCs possessed strong differentiation proficiency, but this proficiency might not mean strong proliferating ability, especially comparing with that of matured tumor cells with CD133 negative expression probably. As there occurred so many kinds of cells in primary lesion and the limitation of only morphological and immunohistochemical observations in this study, the investigation on the both expressions of CD133 and Ki-67 in the same tumor cells should be necessarily considered to carry out in future.
As reported, cancer patients with high CD133 mRNA expression, using a defined cutoff value, showed a decreased survival compared with patients with low or undetectable CD133 expression (21% versus 45% cumulative survival, respectively, after 20 months; P = 0.01). Among patients with metastasis to the bone, cumulative survival was only 22%, compared with 61% for patients with low or undetectable CD133 levels (P = 0.004) . Furthermore, multivariate analysis in their study showed that CD133 expression was an independent predictor for overall survival in patients with bone metastases . At the same time, they compared the level of CD146 mRNA, a pan-endothelial marker, with the level of CD133. CD146 mRNA level was not increased in patients with cancer, nor did CD146 mRNA level correlate with clinical variables or survival . In this study of ours, prognostic analysis based on the different subgroups with or without CD133 protein positivity was assessed by univariate and multivariate evaluations. Univariate assessment revealed that average survival time was (22.76 ± 13.476) months in CD133 positive subgroup while (28.41 ± 18.078) months in negative subgroup. Multivariate analysis showed that, excepting for lymph node metastasis occurrence and later stage of TNM, CD133 protein positivity was also an independent risk factor to survival. Obviously, the detection of CD133 tumor marker regarding as one of the markers of CSCs may be a useful and supplementary means to take a judgment to prognosis of GC.