A Case of KIT-Negative Extra-Gastrointestinal Stromal Tumor of the Lesser Omentum

Abstract

We report the unique case of a 69-year-old man with an extra-gastrointestinal stromal tumor (EGIST) in the lesser omentum. Based on the location of the tumor and the radiological findings, we made a provisional diagnosis of hepatic cavernous hemangioma in the lateral segment. However, after 5 years of follow-up, tumor growth was noted and the patient underwent a laparotomy. The tumor was located in the lesser omentum and resected en bloc with its fused lesser omentum and an adherent portion of the liver. The pathology results indicated an EGIST with microscopic proliferation of epithelioid cells in the lesser omentum; the tumor was immunohistochemically negative for KIT staining and positive for CD34 and PKC theta. Because of the rarity of mitotic figures and the low Ki-67 labeling, the tumor was diagnosed as a KIT-negative EGIST with a low malignant potential. The patient was followed up without receiving imatinib mesylate treatment and has remained free of any signs of recurrence for 26 months. The present case report describes a very rare lesser omental KIT-negative EGIST.

Keywords: Extra-gastrointestinal stromal tumor; KIT-negative; Lesser omentum.

Fig. 1

a CECT shows a 7 × 4 cm hypervascular tumor with heterogeneity located in the lesser omentum (arrow). b CECT shows a lateral cystic component of the tumor enlarged with an internal hemorrhage (arrow).

Fig. 2

a The resected tumor was a 16 cm solid tumor surrounded by a thin pseudocapsule of varying size. b When the tumor was sectioned, the solid component appeared as a whitish-brown, elastically hard mass.

Fig. 3

a Microscopic findings show the proliferation of epithelioid cells with uniformly oval to rounded nuclei and pale eosinophilic cytoplasm, arranged in a sheet-like pattern. b–d Immunohistochemical staining showed the tumor to be negative for KIT (b) and positive for CD34 (c) and PKC theta (d).