BMP4 and cancer: Secretory CAFs highly express secretory proteins, such as various growth factors (e.g., IGF1, PDGFD, FGF7, and VEGFB) that mediate angiogenesis and cancer cell proliferation, some signal molecules (e.g., BMP4 and WNT2B) that are able to maintain cancer stem cell niche, complements (e.g., C1S and C3) and chemokines (e.g., CCL2, CXCL12, and CXCL14) that regulate tumor immunity and inflammation.