Decrease of CD117 expression as possible prognostic marker for recurrence in the resected specimen after imatinib treatment in patients with initially unresectable gastrointestinal stromal tumors: A clinicopathological analysis

Gastrointestinal stromal tumors (GIST) are the most common malignant mesenchymal tumors of the gastrointestinal tract. The principal treatment modality for primary GIST is surgery whereas for metastatic GIST, imatinib has an established role. In patients with locally advanced and metastatic GIST, the role of surgery in the imatinib era is still unclear. Fifteen patients with locally advanced (n≤9) and/or metastatic GIST (n≤6) were treated with imatinib followed by resection. Detailed histopathological examination was performed before and after treatment with imatinib, which was given for a median of 11 months before surgery. Ten patients showed a radiographic partial response, four patients had stable disease, and one patient progressed. At the time of surgery, the median tumor diameter was 6.5g cm. In all the nine patients with locally advanced GIST, a R0 resection could be performed. Histopathological examination showed imatinib effects in all tumors, including the case with progressive disease. All patients with locally advanced disease (n≤9) were alive after a median follow-up of 40 months (range: 18g-59), of which seven patients were free of disease. Four of the six patients treated for metastatic GIST died of disease after 30, 45, 50, and 74 months of follow-up. Remarkably, in five of six patients in whom CD117 expression was diminished or lost in the resection specimen, disease recurrence was observed. In patients with retained CD117 expression, one of the nine patients had recurrent disease. In conclusion, preoperative imatinib treatment in patients with locally advanced GIST resulted in a decrease of tumor load in most patients, enabling complete surgical resection. For patients with metastatic GIST, the role of surgery remains less clear. Loss or decrease of CD117 expression in the resected specimen after imatinib treatment may be associated with disease recurrence.