SPP1 and breast cancer: Soluble and insoluble factors including TGFβ, thrombospondin 1, secreted phosphoprotein 1, colony-stimulating factor 1, and CD73 are expressed by melanoma and breast cancers with EMT and promote Treg infiltration, inhibition of dendritic cell function, and polarization of tumor-associated macrophages (TAMs) into M2 macrophages [30, 33].