[Extragastrointestinal stromal tumors: a report of 4 cases].

Gastrointestinal stromal tumors (GIST) are mesenchymal tumors that arise from the wall of the gastrointestinal tract expressing CD117 and/or the CD34. Similar tumors were described in the soft tissue of the abdomen and are so-called extragastrointestinal stromal tumors (EGIST). We report 4 new cases of EGIST. The tumors occurred in 2 women and 2 men, who ranged in age from 42 to 71 years. Three tumors arose from the soft tissue of the abdominal cavity, and the remainder arose from the retroperitoneum. They ranged in size from 10 to 27 cm. Three cases were composed purely of short fusiform cells tumors, the last case showed an epithelioid pattern. All the tumors expressed CD117. One patient presented with local recurrence and metastasis, one was lost to the follow-up and two patients were doing well. Immunohistochemistry is useful in distinguishing EGIST from other mesenchymal tumors. Intra-abdominal aggressive fibromatosis may express actin and CD117 but catenin is also positive, leiomyosarcoma expresses the actin and/or desmin but CD117 is usually negative, retroperitoneal dedifferentiated liposarcoma is CD117 negative and PS100 positive, inflammatory myofibroblastic tumor is negative for CD117 and CD34. The solitary fibrous tumor expresses CD34 and is negative to CD117. Some tumors expressing CD117 such desmoplastic round cell tumor should not be confused with EGIST. On the occasion of these four observations, we will discuss the clinical aspects and the main differential diagnoses of this tumor.