CD44 can interact with various cytokines, growth factors and extracellular matrix (ECM) secreted by cells in tumor microenvironment.65 The common ligands of CD44 include hyaluronic acid (HA), osteopontin (OPN), chondroitin and so on.66 Among them, HA is the main component of extracellular matrix,67 and its binding with CD44 is cell-specific. The gene discussed is SPP1; the disease is neoplasm.