CD44 and cancer: (iii) Proteoglycans (PGs) in cancer (Supplementary Figure S1.3), including four main types: hyaluronan (HA), chondroitin sulfate proteoglycans (CSPGs), heparan sulfate proteoglycans (HSPGs), and keratan sulfate proteoglycans (KSPGs), were the key bio-molecules in multifarious biological reactions of cancer, such as proliferation, metastasis, adhesion, and angiogenesis [42].