Extra-gastrointestinal stromal tumor of the greater omentum: report of a case and review of the literature

Gastrointestinal stromal tumors (GISTs) represent the majority of primary non-epithelial neoplasms of the digestive tract, most frequently expressing the KIT protein detected by the immunohistochemical staining for the CD117 antigen. Extra-gastrointestinal stromal tumors (EGISTs) are neoplasms with overlapping immunohistological features, occurring in the abdomen outside the gastrointestinal tract with no connection to the gastric or intestinal wall.

We here report the clinical, macroscopic and immunohistological features of an EGIST arising in the greater omentum of a 74-year-old man, with a discussion on the clinical behavior and the prognostic factors of such lesions and a comparison with the gastrointestinal counterpart.

The EGISTs in the greater omentum can grow slowly in the abdomen for a long time without clinical appearance. In most cases a preoperative diagnosis is not possible, and the patient undergoes a surgical operation for the generic diagnosis of "abdominal mass". During the intervention it is important to achieve a complete removal of the mass and to examine every possible adhesion with the gastrointestinal wall. Yamamoto's criteria based on the evaluation of the mitotic rate and the MIB-1 labelling index seems to be useful in predicting the risk for recurrence or metastasis. More studies are necessary to establish the prognostic factors related to localization and size of the EGIST and to evaluate the impact of the molecular characterization as an outcome parameter related to the molecular targeted therapy. In absence of these data, an accurate follow-up is recommended.