Multifaceted roles of CD44 in cancer progression and targeted therapeutic strategies.

CD44, a multifunctional transmembrane glycoprotein, is not only a bystander but also a crucial driver of cancer progression that promotes cancer stem cell maintenance, metastasis, and resistance to therapy. Therefore, CD44 is recognized as a promising therapeutic target in advanced malignancies. Here, we discuss its unique features, such as its structural diversity, which arise from alternative splicing and the post-translational modifications of cleavage and phosphorylation. In addition, we discuss the function of CD44 as a multivalent cell adhesion receptor for extracellular matrix components, including hyaluronic acid, fibronectin, osteopontin, and TSG6, thereby regulating lymphocyte activation, cell-cell interactions, cell adhesion, and migration within the extracellular matrix. Moreover, the emerging role of CD44 as a co-receptor of receptor tyrosine kinases such as epidermal growth factor receptor, c-MET, and vascular endothelial growth factor receptor 2 is highlighted to elucidate the contribution of CD44 to malignant signaling networks. We also discuss its potential as a therapeutic target in advanced cancers, particularly its applications in unconjugated antibodies, antibody-drug conjugates, peptide-based inhibitors, and chimeric antigen receptor-T cell therapies. We conclude by addressing the limitations observed in clinical studies and outlining promising opportunities for future development.