OBJECTIVE We evaluated the characteristics of the gastrointestinal stromal tumors that showed discrepancies between their assessment using the Response Evaluation Criteria in Solid Tumor (RECIST) and Choi's criteria. We also investigated the clinical applicability of Choi's criteria to Korean gastrointestinal stromal tumor patients undergoing imatinib therapy.

METHODS Patients with advanced gastrointestinal stromal tumors treated with frontline imatinib were analyzed. Computed tomography images of these patients were reviewed and genotyping for the KIT and PDGFRA genes was performed. Immunohistochemical staining of c-KIT, CD34, platelet derived growth factor receptor-alpha, platelet derived growth factor receptor-beta, AKT, P-ERK and vascular endothelial growth factor was followed.

RESULTS Ninety-five patients were enrolled. When using Choi's criteria to evaluate the 61 patients who achieved at least partial response by Choi's criteria, 27 patients showed discrepancies in their response to treatment between these two sets of criteria. A lack of CD34 expression in tumors was found to be related to cystic degeneration after imatinib treatment (P=0.001). Patients who showed partial response by Choi's criteria but stable disease by RECIST criteria had a similar progression-free survival to cases who showed a partial response under both systems (P=0.951).

CONCLUSIONS Gastrointestinal stromal tumors showing cystic degeneration after imatinib treatment lack CD34 expression. Choi's criteria have a clinical value in terms of the progression-free survival in Korean patients treated with imatinib.