[Clinical experience of imatinib mesylate for metastatic or recurrent gastrointestinal stromal tumor]

We examined the clinical results of 15 patients treated with imatinib mesylate for metastatic or recurrent gastrointestinal stromal tumors(GIST)at the Osaka City General Hospital. Treatment with imatinib was initiated at 400 mg daily; however, in case of severe adverse events, the dose was gradually reduced to 300 mg or 200 mg to reach a tolerable dose so that administration could be continued for as long as possible. Assessments were performed according to the Response Evaluation Criteria in Solid Tumors(RECIST)and Choi criteria. According to the assessment by the RECIST criteria, clinical response(CR)was observed in 1 patient; partial response(PR), in 5 patients; stable disease(SD), in 6 patients; and progressive disease(PD), in 3 patients; the response rate was 40%. However, as per the Choi criteria, CR was observed in 1 patient; PR, in 11 patients; SD, in 1 patient; and PD, in 2 patients; the response rate was 80%. The median period of progression-free survival was 2,031 days and the 5-year survival rate was 80.0%. Grade 3 or higher adverse reactions observed included leukopenia(1 case), neutropenia( 2 cases), and anemia(1 case). In 6 patients(40%), the dose of imatinib was reduced to 300 mg or less; however, no significant difference in progression-free survival was observed between the 200/300mg group and 400/800mg group. Choi criteria are useful in assessing the response of advanced GIST to imatinib mesylate, and reducing the dose of imatinib mesylate to 200/300mg daily might be sufficient for treating patients who experience severe adverse reactions.