SPP1 and cancer: A diverse set of factors, including TGF-β1, osteopontin (OPN), and interleukin-1β (IL-1β), etc., which are released from cancer cells and/or immune cells,35 induce the transition of stromal fibroblasts to CAFs by regulating the TGF-β and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling pathways.36–39 Then, exosomes also play essential roles in cellular communications, promoting fibroblasts to acquire new receptors or even genetic material from the cancer cells.