Gastrointestinal stromal tumors (GISTs) arise from the interstitial cells of Cajal through gain of function mutations of the oncogene KIT. Imatinib offers the first effective treatment for patients with GISTs, but the therapeutic outcome strongly depends on the type of KIT mutation. We used ProteinChip technology to investigate whether GISTs with different KIT mutations express different proteins. In total, 154 proteins were significantly differentially expressed in GISTs with exon 9 KIT mutation compared to GISTs with exon 11 KIT mutation.