By gene expression analysis, we examined the expression levels of the 4 subunits of the SDH complex; as shown in Fig. 1a, we detected a remarkable down-modulation of SDHC mRNA in GIST_21 with respect to all other GIST samples, both SDHA-mutant and KIT/PDGFRA-mutant GIST. This evidence concerns the gene PDGFRA and gastrointestinal stromal tumor.