CD44 and neoplasm: In tumors, HA is produced by both tumor stroma and tumor cells, and its binding to the cellular receptor CD44 activates intracellular signaling (e.g., PI3K/Akt and Erk pathways, RhoA and Rac, Ras, NF-kB and Src signaling) to promote cell survival, cancer stemness, motility and invasion by cytoskeletal reorganization.