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Year : 2011  |  Volume : 54  |  Issue : 3  |  Page : 618-619
Epithelioid omental extra-gastrointestinal stromal tumor: Report of a case

Department of Anatomic Pathology, Apollo Hospitals, Jubilee Hills, Hyderabad, India

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Date of Web Publication20-Sep-2011

How to cite this article:
Gowrishankar S. Epithelioid omental extra-gastrointestinal stromal tumor: Report of a case. Indian J Pathol Microbiol 2011;54:618-9

How to cite this URL:
Gowrishankar S. Epithelioid omental extra-gastrointestinal stromal tumor: Report of a case. Indian J Pathol Microbiol [serial online] 2011 [cited 2022 Sep 29];54:618-9. Available from:

Gastrointestinal stromal tumors (GIST) occurring outside of the gastrointestinal tract is rare, and form less than 5% of all the GIST, with less than 100 cases being reported in English literature. [1],[2] We report a case of primary extra-gastrointestinal stromal tumor (EGIST) in the omentum.

A 55-year-old male presented with a complaint of abdominal fullness and mild pain of three months' duration. A physical examination revealed a large firm abdominal mass, firm in consistency extending from above the umbilicus to the symphysis pubis. A computed tomography (CT) scan of the abdomen revealed a large mass, about 13 cm in diameter, cystic and solid, with foci of calcification in the region of the omentum. The mass was not adherent to the bladder, bowel loops, liver or spleen. At laparoscopy, a large mass was seen in the omentum, variegated in appearance. The ascitis was minimal. The tumor was removed piece-meal and a complete omentectomy was performed. There was no gross abnormality of the other abdominal organs, including the bowel, liver and spleen.

The tumor was received as four large masses, the largest measuring 13 Χ 10 Χ 5 cm, and the smallest 5 Χ 5 cm. The largest mass had central cystic degeneration with necrotic material within, with calcification [Figure 1]. The cut section of the other masses had a tan white homogeneous fleshy appearance. The microscopy had a variable arrangement of the tumor cells. In areas, the cells were in closely packed sheets, with a network of thin-walled vessels between them; in other areas they were more loosely packed with micro-cystic areas [Figure 2], and in foci, they were seen as sheets of signet ring cells [Figure 3]. The cells were polygonal with a vesicular nucleus having a small nucleolus and a rim of cytoplasm. They were minimally pleomorphic. Mitoses were, however, brisk in the cellular areas, with up to 40/10 high power fields, with occasional abnormal forms. Areas of necrosis were present.
Figure 1: Resected tumor showing a variegated appearance

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Figure 2: Cellular tumor with cells in sheets and with a microcystic appearance in the top left corner (Hematoxylin and eosin, x100)

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Figure 3: Focal areas having signet ring cell morphology (Hematoxylin and eosin, x200)

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Differential diagnoses of mesothelioma, vascular tumors like hemangioendothelioma, EGIST, PEComa, metastaic carcinoma, melanoma, and desmoplastic small round cell tumor were considered. The tumor cells were negative for pancytokeratin, CK 5/6, calretinin, HBME, EMA, desmin, and S100 protein. About 5-10% of the cells were positive for CD34 and 50% of cells for SMA, and they showed diffuse strong cytoplasmic positivity for CD 117 [Figure 4]. A diagnosis of EGIST of the omentum was offered based on the epithelioid cell morphology and CD 117 positivity of the tumor cells.
Figure 4: Strong diff use cytoplasmic positivity for CD117 (IHC, x200)

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Extra-gastrointestinal stromal tumors are rare, comprising <5% of all GIST, and hence, there are only very few series of reports, comparing them to gastrointestinal stromal tumor GIST. [3] The diagnosis of EGIST is often unexpected and as in the case described, the light microscopic features can be confounding. However, in epithelioid tumors, a mixed pattern, including cellular, microcystic, and signet ring areas, the mitoses being out of proportion to the pleomorphism, and the relatively bland nuclei are clues to the diagnosis. [4] The differential diagnosis should include other omental tumors, notably epithelioid mesothelioma, metastatic carcinoma, mesenchymal tumors including hemangioendothelioma, desmoplastic small round cell tumors, which can lack desmoplasia and have varying patterns, and melanoma. A battery of immune stains is therefore necessary for confirmation of diagnosis. The panel of markers as in this case, should include pancytokeratin, calretinin or other mesothelioma markers, like desmin, S100, CD31, and CD34, all of which will be negative, except CD34, which is almost always positive. CD117 positivity will clinch the diagnosis.

   References Top

1.Miettinen M, Lasota J. Gastrointestinal stromal tumours-definition, clinical, histological, immunohistochemical, and molecular genetic features and differential diagnosis. Virchows Arch 2001;438:1-12.  Back to cited text no. 1
2.De Mates RP, Lewis JJ, Lewing D, Mudon SS, Woodrnff JM, Brennan MF. Two hundred gastrointestinal stromal tumours: Recurrence patterns and prognostic factors for survival. Ann Surg 2000;231;51-8.  Back to cited text no. 2
3.Miettinen M, Monihon JM, Sarlomo-Rikala M, Kovatich AJ, Carr NJ, Emory TS, et al . Gastrointestinal stromal tumours/smooth muscle tumours (GISTs) primary in the omentum and mesentery: Clinicopathologic and immunohistochemical study of 26 cases. Am J Surg Pathol 1999;23:1109-18.  Back to cited text no. 3
4.Reith JD, Goldblum JR, Lyles RH, Weiss SW. Extragastrointestinal (soft tissue) stromal tumours: An analysis of 48 cases with emphasis on histologic predictors of outcome. Mod Pathol 2000;13:577-85.  Back to cited text no. 4

Correspondence Address:
Swarnalata Gowrishankar
Department of Anatomic Pathology, Apollo Hospitals, Jubilee Hills, Hyderabad - 500 033
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0377-4929.85118

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4]

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