PDGFRA and melanoma: The basal plasma levels of PDGF were approximately 100-fold greater than those of the other growth factors examined in our panel, and, comparing the ordinate scale of panel B to the scaling in panel A and panel C, we conclude that transient AR42 exposure causes the further evolution of MEL28-R melanoma cells that are very likely becoming addicted to the signaling downstream of the PDGFRα/PDGFRβ/FGFR/c-MET/prolactin receptors.