They secrete TGF-β, leukemia inhibitory factor (LIF), growth arrest-specific protein 6 (GAS6), fibroblast growth factor 5 (FGF5), growth differentiation factor 15 (GDF15), and hepatocyte growth factor (HGF), which drive the invasive and proliferative behaviors in cancer cells (102–107). Here, GDF15 is linked to cancer.