PDGFRA and neoplasm: The CAFs expressed FSP1, but not GIST markers by IF staining and immunoblotting analysis, whereas GIST-T1 (T1) (KIT exon 11 mutant) [27] and primary tumor cells (from a KIT-expressing PDGFRA mutant GIST) did not express FSP1 (Fig. 1c; Supplementary Fig. 1a).