FAP and neoplasm: However, stromal cells supporting the development of PDAC in humans are recognized to be essentially cancer-associated fibroblasts deriving from mesenchymal stem cells or pancreatic stellate cells, which produce collagen and hyaluronan-based ECM and bear various specific surface proteins (a-SMA, FSP-1, FAP-a, PDGFR-b, SPARC...), whose activation/suppression can lead to either tumor suppression or promotion, particularly through the modulation of ECM stiffness13–15.