CD44 and cancer: The secretion of MMP-2 and MMP-9 in the cancer cells can be promoted by HA treatment, and this is believed to be related to the HA-CD44-Ras-MEK1-MAPK signaling pathway because the effect of HA could be inhibited by anti-CD44 antibody, Manumycin A and mitogen-activated protein kinase (MAPK) or mitogen-activated protein kinase kinase-1 (MEK-1) inhibitor (PD98059) [13].