CD44 and lung cancer: CD44 exists in a variety of cells like cancer stem cells (glioma cells [65], lung cancer cells [66], breast cancer stem cells [67], liver cancer cells [68], gastric cancer cells [69]), normal stem/progenitor cells (embryonic stem cells [70], neural stem cells [71], intestinal stem cells [72]), epithelial cells [73], vascular smooth muscle cells [74] and endothelial cells [75, 76], mediating the HA regulation of cell adhesion, proliferation, differentiation, migration and metabolism.