PRG4 and cancer: While PRG4 is more of a mucin-like glycoprotein versus a classic proteoglycan per se, other proteoglycans can act directly or indirectly to affect multiple signalling axes, including the TGFβ pathway, leading to positive or negative regulation of multiple cellular processes such as angiogenesis, cell migration and invasion of diverse types of cancer cells and in a context-dependent manner [47,48].