Nonetheless, although the presence of VEGFR-1 is necessary for a number of tumors to respond to the anti-PlGF therapy [231], the direct inhibition of VEGFR-1 does not always replicate the effects obtained with the anti-PlGF therapy in other tumor models [241], thus suggesting an alternative signaling mechanism for PlGF, independently from the presence of VEGFR-1. Here, PGF is linked to neoplasm.