 Medical history, current medication, weight, height, and ECOG performance status are recorded prior to study entry. Physical examination, blood cell counts, blood biochemistry, pregnancy test, chest X-ray or CT, and CT or MRI of the abdomen and pelvis are carried outmeasured prior to study entry. FDG-PET is an optional staging examination. Research serum samples are collected for banking prior to initiating imatinib and at 6-month intervals during the study. Tumor tissue is reviewed centrally to confirm the histological diagnosis of GIST, and KIT and PDGFRA gene mutation analyses will be performed from stored GIST tissue. 