CXCL12 and neoplasm: MSCs' paracrine immunoregulatory capabilities through chemokines, cytokines, and growth factors such as stromal cell-derived factor 1 (SDF-1), IL-6, tumor growth factor- (TGF-) β, tumor necrosis factor-inducible gene 6 protein (TSG-6), and metabolites [20] as well as their cell-cell contact impact tumor growth and treatment [21].