[A case of extragastrointestinal stromal tumor with peritoneal dissemination].

Here, we present the case of a 60-year-old man in whom abdominal computed tomography showed a solid abdominal tumor (11 cm in diameter) in the pelvic space, with widely disseminated nodular lesions. Emergency surgery was performed following the rapid onset of intense abdominal pain. Peritoneal disseminations were widespread and the tumor was confirmed to be in the pelvic space. The tumor was not connected to any segment of the intestinal tract but rather to the retroperitoneum. Immunohistochemical staining was positive for c-kit (exon 11 mutation) and CD34 but negative for S-100 protein. Careful postoperative examination did not reveal any lesions in the upper or lower alimentary tract. On the basis of these findings we diagnosed the tumor as an extragastrointestinal stromal tumor (EGIST) originating from the retroperitoneum. After surgery, intravenous infusion of imatinib was started at a full dose of 400mg/day; however, owing to strong adverse effects, the dose was reduced to 200mg/day. Despite halving the dose, the patient has remained lesion-free according to computed tomography for 36 months after the operation. Low-dose imatinib chemotherapy remained efficacious in controlling progression in this case.