Extragastrointestinal stromal tumors of the omentum: review apropos of a case with a novel gain-of-function KIT mutation.

Introduction: We describe a case of extragastrointestinal stromal tumor (EGIST) of the omentum harboring a novel KIT mutation and review the literature on omental EGISTs, emphasizing on molecular genetic data.

Case Presentation: A large EGIST arising from the lesser omentum was incidentally diagnosed in a 68-year-old man during emergency laparotomy for intra-abdominal hemorrhage following a car accident. The tumor was composed of CD117+/CD34+ spindle-shaped cells with low mitotic activity. Analysis of tumor DNA revealed a heterozygous duplication of 30 bp in exon 11 of KIT. Nine months after R0 resection, positron emission tomography showed abnormal uptake in the upper abdomen. The patient was treated with imatinib mesylate and is alive and well 2 years after the operation.

Discussion: Omental EGISTs remain silent despite a large tumor size. They are diagnosed at a median age of 65 years and show low proliferative activity in the majority (about 80%) of cases. Although the median follow-up period of published cases is only 20 months, mortality appears to be low after R0 resection and is expected to decrease further following the recent introduction of imatinib therapy for high-risk tumors. Accumulating molecular genetic data may lead to improved prognostic classification and patient management.