An invasive extragastrointestinal stromal tumor curably resected following imatinib treatment.

Extragastrointestinal stromal tumors (EGISTs) are rare tumors located outside the gastrointestinal tract. While curable resection is accepted as a noninvasive EGIST treatment, the therapeutic strategy for invasive EGISTs has not yet been established. The present report is the first to show a case of invasive EGIST completely resected after downsizing the tumor with imatinib treatment. A 69-year-old female had multiple masses adjacent to the stomach and ileocecum. The primary lesion measured 18 cm in size and had invaded the stomach, pancreas and liver. The histological findings of fine-needle aspiration samples revealed a proliferation of dysplastic spindle cells that exhibited immunoreactivity for anti-c-kit antibodies. The masses were therefore diagnosed as multiple GISTs with invasion to other organs, with origin difficult to determine at the time. Nineteen months after the imatinib treatment, the tumors were downsized and distinct from the stomach, pancreas and liver. Accordingly, the tumors were regarded to be EGISTs derived from the mesentery. Because they slightly regressed 26 months after treatment, surgery was applied to remove the EGISTs. The intraoperative findings showed no invasive signs, and the tumors were completely removed. The histological findings revealed the presence of dysplastic and c-kit-positive spindle cells in the tumor with an MIB-I index of more than 5%, resulting in a final diagnosis of high-risk EGIST derived from the mesentery. No recurrence was detected for 16 months after resection. In conclusion, preoperative treatment with imatinib followed by curable resection is a feasible option to cure invasive EGISTs.