Platelet-derived growth factors (PDGFs) and their receptors were identified and purified decades ago.PDGFs are important during normal development and in human cancers.In particular,autocrine PDGF signaling has been implicated in various types of malignancies such as gliomas and leukemia.In contrast,paracrine signaling was found in cancers that originate from epithelial cells,where it may be involved in stromal cell recruitment,metastasis,and epithelial-mesenchymal transition.This editorial briefly discusses autocrine and paracrine PDGF signaling and their roles in human cancers,and introduces a series of review articles in this issue that address the possible roles of PDGFs in various processes involved in different types of cancers.