PGF and neoplasm: Furthermore, distinct myeloid cell populations including macrophages, immature monocytic and granulocytic myeloid derived suppressor cells are recruited to the tumor by specific cytokines and contribute to the resistance to VEGF inhibition via the production of alternative CAF such as angiopoietin-2 (Ang2), granulocyte colony-stimulating factor (GCSF) and placental growth factor (PlGF) [9, 11].