PLD1 and osteosarcoma: ECs promote osteosarcoma progression by secreting Von Willebrand factor (VWF) and activating NF-κB signaling, which contributes to epithelial-mesenchymal transition (EMT) and metastasis; OS cells in turn activate phospholipase D1 signaling to promote VWF release by ECs, resulting in further tumor deterioration (29).