Omental milky spots in screening gastric cancer stem cells.

The existence of cancer stem and progenitor cells in solid tumors has been widely postulated. However, neither the cancer stem cells nor the cancer progenitor cells have been definitively identified and functionally characterized. Here we propose a new strategy to identify and isolate gastric cancer stem cells -using omental milky spots to screen gastric cancer stem cells in peritoneal metastasis mouse models of gastric cancer. In this study, we used the property that the macrophages in omental milky spots are cytotoxic against tumor cells and so able to screen and collect cancer stem cells. Our findings suggest that macrophages in omental milky spots have not only cytotoxic properties against tumor cells but also provide a microenvironment within milky spots in which cancer stem cells are capable to survive and grow into micrometastasis. Omental milky spot become a cancer stem cell niche in this situation. Further we studied the omental milky spots for screening gastric cancer cells (OMSS-GCCs) and found that omental milky spot enriched the volume of gastric cancer stem cells. Tumors were consistently generated after an injection of 1×103 OMSS-GCCs. OMSS-GCCs high express CD133 and low express CD324. Omental milky spots are a highly efficient "natural filter" for screening gastric cancer stem cells.