CD44 and neoplasm: One possible explanation for this tumor-specific localization is that the healthy mesothelium is protected by a layer of anti-adhesive proteoglycans, whereas tumor disruptions expose the underlying basement membrane, revealing extracellular matrix substrates (e.g., collagen I/IV, fibronectin, hyaluronan, and laminin) that can be bound by CD44 [26] and α5β1 integrins [27] expressed by the HB1.F3.CD.21 NSCs.