The 3D projections in both PCA analyses showed that SDH-deficient GISTs distinctly separate from KIT-mutant GISTs, providing proof of an expression profile typical of this molecular subgroup and profoundly different from KIT-mutant GISTs, supporting the hypothesis that the two GIST molecular groups may derive from two distinct cell types or oncogenic programs (Figure 1A,B). This evidence concerns the gene SDHB and gastrointestinal stromal tumor.