PGF and cancer: They include VEGF-A, soluble VEGFR-2 (sVEGFR-2), and placenta growth factor (PlGF; a member of the VEGF family and a specific ligand of VEGFR-1 [18]), all of which are components of the angiogenesis system [10,11,19] and which have previously been reported as circulating factors that are modulated in cancer patients treated with sunitinib [14,20].