[A Case of Giant GIST Originating from the Greater Omentum].

A 60-year-old woman was admitted for abdominal distention, abdominal pain, and anorexia. Abdominal CT showed a 30×20 cm mass with contrast effect. gastrointestinal stromal tumor(GIST) of the omentum or the mesenterium was suspected. Peritoneal nodules were also recognized. We performed palliative surgery. The tumor was considered to have originatedfrom the greater omentum andinvolvedthe marginal artery of the transverse colon. We performedpartial excision of the transverse colon andresection of the tumor. Immunohistochemically, the tumor cells were c-kit(+), CD34(+), S100(-), andDOG1(-), with 1 fission image for 50 fields of view with high magnification. The patient was diagnosed with high-risk GIST originating from the greater omentum. The patient was started on imatinib administration on the 37th day but died on the 109th day.