We report two cases of giant gastrointestinal stromal tumor (GIST) of the omentum. Case 1: A 63-year-old man developed intraperitoneal hemorrhage during hospitalization for an abdominal tumor was treated by emergency resection of the tumor. The tumor arised from the omentum and was not adherent to the surrounding tissues. And perforation was identified in the right side of the tumor. Case 2: A 79-year-old woman complaining of abdominal pain was detected to have an abdominal tumor in the right lower quadrant of the abdomen. At laparotomy, we found a huge and a small tumors continued to the omentum, and resected these tumors. Immunohistopathological examinations revealed that these tumors stained positively for c-kit, and were diagnosed as GIST. All tumors showed positive response in immunostaining for Ki-67, suggesting a potent proliferating ability of them. Actually intraabdominal metastasis was confirmed at the time of laparotomy in the both cases.
Recently imatinib mesylate has been administered for the treatment of GIST, however, from the standpoints of adverse side effects and long-term use, the safety of the regimen has not been established as yet. Granted that GISTs become huge, those tumors tend to be less invasive to surrounding organs, so that surgical excision would be desirable if it is possible.