RESUMEN
BACKGROUND: Gastrointestinal stromal tumors are uncommon intra-abdominal tumors. In fewer than 5% of cases, they originate primarily from the mesentery, omentum or peritoneum and these extra-gastrointestinal stromal tumors tend to have characteristics similar to gastrointestinal stromal. CASE REPORT: We report a case of extra-gastrointestinal stromal tumor in a 76-year-old male, Eastern Cooperative Oncology Group (ECOG) performance status of 2. Abdominal Computed Tomography (CT) showed multiple non-homogeneous confluent nodules at the level of the greater omentum and mesentery, involving the bladder and rectum, with additional peritoneal nodules in the upper abdomen. In March 2008, the patient started imatinib mesylate at 400 mg/day. Instrumental examinations showed progressive response until thoracic-abdominal CT in February 2012 which documented a complete response. Follow-up ended in October 2013. Treatment with imatinib, in addition to pathological response, provided clinical benefit, a progressive regression of symptoms and improved the patient's ECOG performance status from 2 to 0.