A multinational phase II clinical trial of neoadjuvant imatinib for large gastrointestinal stromal tumor of the stomach

130 Background: Neoadjuvant therapy is expected to reduce the risk of primary surgery, such as rupture of the tumor, hemorrhage, and multi-visceral resection, and to improve survivals for patients with a large gastric gastrointestinal stromal tumor (GIST). This study aims to evaluate the efficacy and safety of neoadjuvant imatinib therapy for a large gastric GIST. Methods: Patients with gastric GIST, which is 10cm or larger and without metastasis, received neoadjuvant imatinib (400mg/day) for 6 months, and up to 9 months if maximal response is expected. Postoperative adjuvant imatinib was prescribed for at least 1 year and up to 3 years according to adjuvant treatment guideline. The primary endpoint was complete (R0) resection rate. A primary analysis were performed by the time all the operations were finished, to examine the efficacy and safety of the neoadjuvant treatment. Results: Between Feb 2010 and Sep 2014, 55 patients were enrolled in Japan and Korea. One patient with a jejunal GIST and one patient with PDGFRA-18 D842V mutation were excluded from analysis. Mean tumor diameter was 12cm (10-23). 86.8% of patients (46/53) completed neoadjuvant treatment. Dose reduction of imatinib was performed in 26.4% (14/53). The most frequent Grade 3 or 4 adverse events were G3 rash (5/53, 9.4%) and G3/4 neutropenia (4/53, 7.5%). Disease control rate (PR+SD) and response rate (PR) of neoadjuvant imatinib was 100% and 62.3% by RECIST, and 100% and 98.1% by Choi criteria, respectively. There was no case of CR or PD. 50 patients underwent operation, and R0 resection rate was 90.6% (n = 48, 95% CI 79.3% - 96.9%), which was significantly higher than the threshold value of 70% (p < 0.001). Combined resection of other organs (except gall bladder) was performed in 24.5% (n = 13), and 83.0% of patients (n = 44) could preserve ≥ 50% of the stomach. Postoperative complication occurred in 18.0% (9/50). Conclusions: Neoadjuvant imatinib treatment is effective and safe treatment option for a large primary GIST allowing high R0 resection rate with acceptable incidence of adverse events and postoperative complications. Clinical trial information: UMIN000003114.