SPP1 and neoplasm: Moreover, a variety of tumor products can serve to attract mast cells into the tumor microenvironment (TME) (Figure 1), including stem cell factor (SCF) [43,44], vascular endothelial growth factors (VEGFs) [45,46], angiopoietin 1 (ANGPT1) [47], several chemokines (CXCL8, CXCL2, CXCL1, and CXCL10) [46,48,49], prostaglandin E2 (PGE2) [50,51], TSLP [52], and osteopontin [53].