Cancer stem cells, also known as tumour initiating cells, refer to a small side population of tumour cells with unlimited self-renewal activity and potentially promote the formation of tumour, according to the cancer stem cell (CSC) hypothesis that has emerged recently [
28‐
32]. There is currently heightened interest in the utility of using CD133 as a marker to identify the tumor stem cell population for a variety of malignancies [
3‐
5,
8] Recently, CD133 was found to be highly expressed in more or equal to 50% of gastric, pancreatic and intrahepatic cholangiocarcinomas [
10]. Quantitative flow cytometric analysis showed that a panel of established gastric cancer cell lines expressed CD133 at levels higher than normal epithelial cells. However, it has also been found that CD133 expression is not restricted to stem cells, and both CD133+ and CD133- metastatic colon cancer cells initiate tumors [
33,
34]. A murine anti-human CD133 antibody conjugated to a potent cytotoxic drug, monomethyl auristatin F (MMAF), effectively inhibited the growth and induced apoptosis of KATO III gastric cancer cells in vitro [
10]. Therefore, anti-CD133 antibody-drug conjugates may warrant further evaluation as a molecular therapeutic strategy to eradicate CD133-positive tumour cells in gastric cancer. CD133 expression as a prognostic marker has been found in colorectal cancer [
11‐
18] and brain tumours [
19‐
21], although it is still controversial for ovarian cancer and non-small cell lung cancer. There are no reports on the prognostic significance of CD133 expression or correlation with Ki-67 in gastric cancer. In this study the positive expression of CD133 is found in 57.4% and is closely related to the worst prognosis of gastric adenocarcinoma. Our results indicate that the expression of CD133 may be involved in tumor size, invasive depth and histological grade of gastric tumor, which are in agreement with previous reports on colorectal cancer [
16,
17]. In this research, the expression of CD133 positively correlates with the shorter survival time, suggesting CD133-positive cells may contain more cancer stem-like cells. Thus residual cancer stem-like cells after routine therapy may lead to tumour recurrence and metastasis through the self-renewal and multilineage differentiation with agreement of cancer stem cell hypothesis [
35,
36]. It implies that CD133 may be one of the specific molecular markers in prognosis of gastric adenocarcinoma. The results of our study, that Ki-67 expression corresponds with tumor size, degree of differentiation, depth of invasion, lymphatic metastasis, TNM staging and prognosis, are associated with a previous report [
37]. This research also shows that CD133 positively correlates with Ki-67, implying higher putative proliferative activity in CD133-positive cancer cells, which corresponds with the results from Ieta, et al. [
35]. Taken together, CD133 is highly expressed in the cancer cells of gastric adenocarcinoma. The combined detection of CD133 and Ki-67 expression, to some extent, can reflect the biological behavior of gastric cancer cells, thus guiding the choice of chemotherapy and molecular targeting therapy.