Utility of FDG-PET for early evaluation of efficiency of imatinib mesylate (Glivec) in the treatment of gastrointestinal stromal tumors

The management of gastrointestinal stromal tumors, usually defined as c-KIT-positive mesenchymal neoplasias, has evolved very rapidly in the last five years. Imatinib mesylate (Glivec(R)) is the standard treatment in unresectable or metastatic gastrointestinal stromal tumors. Imatinib should be given until development of intolerance or progressive disease. It is not uncommon for gastrointestinal stromal tumors to become larger during the early post-treatment phase and conventional response to treatment criteria in solid tumors have a limited value for evaluation the efficiency of imatinib in this period. FDG-PET has proven to be highly sensitive in detecting early response tumor. A 53-year old woman was diagnosed of relapsed gastrointestinal stromal tumor 18 months after adyuvant imatinib mesylate finished. Imatinib was started and 72 hours later the tumor showed a decrease of fluorodeoxyglucose F18 uptake on positron emission tomography scan.