AIM: To evaluate and characterize selleck kinase inhibitor the patterns of disease progression of metastatic or unresectable gastrointestinal stromal tumor (GIST) treated with imatinib mesylate, and to determine the prognostic significance associated with disease progression. METHODS: Clinical data and computed tomography (CT) images were retrospectively reviewed in 17 GIST patients who were treated with imatinib mesylate from October 2002 to October 2006. Apart from using size measurement for evaluation of tumor response [Response Evaluation Criteria in Solid Tumors (RECIST) criteria], patterns of CT changes during treatment were evaluated and correlated with clinical data. RESULTS: There were eight non-responders and nine responders.

Five patterns of CT change during treatment were found: focal progression (FP), generalized progression (GP), generalized cystic change (GC), new cystic lesion (NC) and new solid lesion (NS). At the end of study, all non-responders showed GP, whereas responders showed cystic change (GC and NC) and response according to RECIST criteria. Overall survival was significantly better in patients with cystic change or response within the RECIST criteria compared with GP patients (P = 0.0271). CONCLUSION: Various patterns of CT change in patients with GIST who responded to imatinib mesylate were demonstrated, and might determine the prognosis of the disease. A combination of RECIST criteria and pattern of CT change are proposed for response evaluation in GIST.

Keywords: Computed tomography, Gastrointestinal stromal tumor, Imatinib mesylate INTRODUCTION Gastrointestinal stromal tumors (GISTs) are uncommon neoplasms that arise from mesenchymal cells in the walls of the gastrointestinal tract and account for 0.1%-3.0% of all gastrointestinal neoplasms and 5.7% of sarcomas[1,2]. GISTs arise most often from the stomach (60%-70%), followed by small intestine (20%-25%), but rarely from the rectum (5%), esophagus, colon or appendix[3]. GISTs differ from the other mesenchymal neoplasms histopathologically by immunohistochemical expression of CD 117 (c-kit proto-oncogene)[4]. Surgical resection is the standard initial treatment for non-resectable GISTs. However, locally advanced and metastatic tumors of the peritoneum or liver can effectively be treated with imatinib mesylate (known as Gleevec in the United States, Glivec in the rest of the world, and previously referred to as STI 571; Novartis Pharmaceuticals, Basel, Switzerland), a selective-tyrosine kinase inhibitor[5,6]. The drug acts as a c-kit blocker and is highly effective in patients with advanced disease[7], with nearly half of the patients responding to Entinostat treatment[8]. For optimal clinical outcome, the accurate assessment of tumor response to imatinib mesylate has become important.