CD44 and breast cancer: Breast CSCs produce high levels of HA; HA promotes the interaction of breast CSCs with tumor-associated macrophages to activate other stromal cells that augment the growth of CSCs; Excessive HA production promotes acquisition of CSC properties via Twist and the TGF-β-Snail signaling axis in breast cancer; HA-CD44 interaction induces Nanog-Stat-3 interaction, resulting in multidrug resistance in breast and ovarian cancer; HA–CD44 interaction stimulates stem cell marker expression, stemness properties and chemoresistance in head and neck CSCs.