Activity and side effects of imatinib in patients with gastrointestinal stromal tumors: data from a german multicenter trial

Gastrointestinal stromal tumors (GIST) are mesenchymal tumors that in the past were classified as leiomyosarcomas or leiomyomas not responding to standard sarcoma chemotherapy. In several phase I and II trials the efficacy and safety of imatinib was shown before the largest trial ever performed in a single sarcoma entity revealed response rates (CR/PR) of 52%. This multicenter phase II trial presented here was performed to open access to imatinib for patients with unresectable or metastastatic GIST when the EORTC 62005 trial had been closed before imatinib was approved in Germany. It was designed to follow the best clinical response and to assess the efficacy, safety and tolerability of imatinib 400 mg/d in patients with unresectable or metastatic gastrointestinal stromal tumor. 95 patients were treated in this trial with Imatinib 400 mg/d. Four patients (4.6%) attained a complete response and 26 patients (29.9%) a partial response to imatinib treatment. Forty-one patients (47.1%) revealed a stable disease and 16 patients (18.4%) had a progressive disease. Of the progressive patients 22% showed a partial response and 67% showed stable disease after escalating the dose to 800 mg. According to SWOG tumor response classification, 66 patients (70%) were free of progression within the first year of treatment. Seventy-one patients (74.7%) experienced adverse events or severe adverse events with a suspected relationship to the study drug. Among these, the most common were nausea (n = 27 patients, 28.4%), eyelid edema and peripheral edema in 23 patients each (24.2%), diarrhea in 20 patients (21.1%), muscle cramps in 15 patients (15.8%) and fatigue in 13 patients (13.7%). Imatinib 400 mg/d led to disease stabilisation in 81,6% of patients with unresectable or metastatic malignant GIST. Thirty-four percent of patients attained a tumor remission (partial or complete response). The safety profile of imatinib based on adverse event assessment is favorable. Imatinib is generally well tolerated in patients with gastrointestinal stromal tumors.