Extragastrointestinal stromal tumour (EGIST) presented as a mesenteric and retroperitoneal mass

Extragastrointestinal stromal tumour (EGIST) occurs outside the gastrointestinal tract and has histopathological and molecular characteristics similar to gastrointestinal stromal tumour (GIST). This tumour is rare and aggressive. A male patient was admitted with anaemia and lower limb oedema. CT scan showed a tumour in the mesentery and retroperitoneum, suspected to be a small bowel GIST. During laparotomy an unresectable mass was found compressing the retroperitoneal structures. Pathology and immunohistochemistry (CD117) confirmed an EGIST. EGIST arises from Cajal-like cells or from pluripotent stem cells outside the gastrointestinal tract. It is aggressive and has a worse prognosis than GIST. Immunohistochemistry is crucial for diagnosis. Surgery aimed at debulking as much of a tumour mass as possible is the cornerstone of treatment. The role of imatinib is not clear. EGIST is rare and has a bad prognosis, and there is no consensus on grading and management. A low threshold of suspicion is crucial for early diagnosis.