PDGFC and gastrointestinal stromal tumor: Finally, IF staining of human PDGFRA and KIT mutant GIST sections showed that cells expressing PDGFC were juxtaposed to cells with colocalized expression of activated PDGFRA and SLUG, implying that PDGFRA activation by PDGFC in GIST is associated with SLUG expression (Supplementary Fig. 5i).