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Extragastrointestinal stromal tumors, by definition, arise from outside the GI tract but histologically resemble their GI counterparts. In general, they are an aggressive group of tumors sharing a similarity to GI stromal tumors (GIST) arising in the distal GI tract. One of the larger studies of 48 cases found a female predominance (32F 16M) with an age range of 31-82 years (mean 58 years). The majority arose from the soft tissue of the abdominal cavity while the remainder arose from the retroperitoneum. The size ranged from 2-32 cm.

Under the microscope, the tumors showed characteristic changes of GIST with tumors having rounded epithelioid cells to spindled cells with a fine fibrillary background and varying amounts of myxoid and hyalinized stroma. Immuhohistochemical analysis revealed the following staining pattern:

Immunostain Percentage
CD117 (c-kit receptor) 100%
CD34 50%
Neuron-specific enolase (NSE) 44%
Smooth muscle actin (SMA) 26%
Desmin 4%
S-100 protein 4%

Like the GIST, these tumors consistently exhibit staining for CD117. Follow-up for 31 patients revealed metastases in 12 patients (39%). High cellularity, mitotic activity (>2 per 50 hpf), and necrosis were associated with a statistically significant increased risk for an adverse outcome. Further stratifying this group found only 5% of patients who had none or one of the poor prognostic factors experienced an adverse outcome versus 92% of patients who had 2 or 3 features. Although size has been noted to be an important factor in GIST, there were too few cases that were very small (<5 cm) that allowed for adequate evaluation.


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Primary malignant gastrointestinal stromal tumor of the liver.

Hu X, Forster J, Damjanov I.

Department of Pathology, The University of Kansas School of Medicine, Kansas City, Kan 66160-7410, USA.
Arch Pathol Lab Med. 2003 Dec;127(12):1606-8. Abstract quote  

We report the case of a malignant, primary, hepatic gastrointestinal stromal tumor (GIST) that was resected from the liver of a 79-year-old woman.

To our knowledge, this is the first primary, hepatic GIST on record. The tumor expressed CD117 (c-Kit protein) and vimentin and had the ultrastructural features of GISTs. Sixteen months after partial hepatectomy and resection of the tumor, a hilar lymph node metastasis was found. The metastatic tumor had the same morphologic features as the primary tumor, but in addition it contained numerous multinucleated giant cells.

This case shows that GIST can occur as a primary liver tumor, and accordingly, we point out that not all hepatic tumors with a GIST phenotype should be automatically considered to be metastases from a primary gastrointestinal site.

Gastrointestinal stromal tumors/smooth muscle tumors (GISTs) primary in the omentum and mesentery: clinicopathologic and immunohistochemical study of 26 cases.

Miettinen M, Monihan JM, Sarlomo-Rikala M, Kovatich AJ, Carr NJ, Emory TS, Sobin LH.

Department of Soft Tissue Pathology, Armed Forces Institute of Pathology, Washington, DC 20306-6000, USA.

Am J Surg Pathol 1999 Sep;23(9):1109-18 Abstract quote

Gastrointestinal stromal tumor or smooth muscle tumor (GIST) is the designation for a major subset of gastrointestinal mesenchymal tumors that histologically, immunohistochemically, and genetically differ from typical leiomyomas, leiomyosarcomas, and schwannomas. Because GISTs, like the interstitial cells of Cajal, the gastrointestinal pacemaker cells, express CD117 (c-kit protein), the origin of GISTs from the interstitial cells of Cajal has been recently proposed. Comparison of GISTs primary in the omentum and mesentery to GISTs primary in the tubular gastrointestinal tract is of particular diagnostic and histogenetic interest in view of the possible similarity of these tumors with the GIST group.

In this study, we analyzed 14 omental and 12 mesenteric primary mesenchymal tumors representing smooth muscle tumors or GISTs. These tumors were phenotypically compared with gastric and small intestinal GISTs, leiomyomas of the esophagus, and leiomyosarcomas of the retroperitoneum. Most (13 of 14) omental and mesenteric (10 of 12) tumors showed histologic features similar to GISTs with elongated spindle cells or epithelioid cells with high cellularity; most of these tumors showed low mitotic activity. Omental and mesenteric GISTs were typically positive for CD117 and less consistently for CD34. They often showed alpha-smooth muscle actin reactivity but were virtually negative for desmin and S-100 protein. One omental and two mesenteric tumors showed features of leiomyosarcoma with ovoid, less elongated nuclei, cytoplasmic eosinophilia; all these tumors had significant mitotic activity. These tumors were positive for alpha-smooth muscle actin and two of them for desmin, but all were negative for CD34 and CD117, similar to retroperitoneal leiomyosarcomas. Tumor-related mortality occurred in the group of mesenteric GISTs, but not in the group of omental GISTs. In contrast, all three patients with a true leiomyosarcoma of the omentum or mesentery had documented liver metastases or died of tumor.

In summary, we show that tumors phenotypically identical with GISTs occur as primary tumors in the omentum and mesentery. The occurrence of CD117-positive tumors outside the gastrointestinal tract militates against an origin of these tumors exclusively from the interstitial cells of Cajal.



Out Extragastrointestinal (soft tissue) stromal tumors: an analysis of 48 cases with emphasis on histologic predictors of outcome.

Reith JD, Goldblum JR, Lyles RH, Weiss SW.

University of Florida, Gainesville, USA.

Mod Pathol 2000 May;13(5):577-85 Abstract quote

The clinicopathologic features of 48 tumors that were histologically similar to gastrointestinal stromal tumors but occurred in the soft tissues of the abdomen were analyzed to determine their overall similarity to their gastrointestinal counterpart, their biologic behavior, and the parameters that predict risk for adverse outcome.

Classic leiomyomas and leiomyosarcomas were specifically excluded. The tumors occurred in 32 women and 16 men, who ranged in age from 31 to 82 years (mean, 58 years). Forty tumors arose from the soft tissue of the abdominal cavity, and the remainder arose from the retroperitoneum. They ranged in size from 2.1 to 32.0 cm and varied from tumors composed purely of rounded epithelioid cells to those composed of short fusiform cells set in a fine fibrillary collagenous background with some cases showing a mixed pattern.

Tumors displayed variable amounts of stromal hyalinization, myxoid change, and cyst formation. The tumors expressed CD117 (c-kit receptor) (100%), CD34 (50%), neuron-specific enolase (44%), smooth muscle actin (26%), desmin (4%), and S-100 protein (4%). Tumors were evaluated with respect to several parameters: size (<10 cm or >10 cm), cellularity (low or high), mitoses (0 to 2 per 50 high-power fields, >2 per 50 high-power fields), nuclear atypia (1 to 3+), cell type (epithelioid, spindled, or mixed), and necrosis (absent or present). These parameters were then evaluated in univariate and multivariate analysis with respect to adverse or nonadverse outcome, the former defined as metastasis or death from tumor.

Follow-up information was obtained for 31 patients (range, 4 to 84 months; median, 24 months). One patient presented with an adverse event and, therefore, was excluded from subsequent analysis. Twelve patients (39%) developed metastases or died of tumor. In univariate analyses, cellularity, mitotic activity (>2 per 50 high-power fields), and necrosis were associated with statistically significant increases in the risk for adverse outcome. Despite the relatively small sample size, in a multivariable analysis mitotic activity (relative risk, 7.46; P = .09) and necrosis (relative risk, 3.75; P = .07) displayed trends toward independent predictive value. No association was noted between histologic pattern and outcome. Although only 39% of tumors behaved in a malignant fashion, this figure probably represents a conservative estimate because long-term follow-up (>5 years) was available for only a limited number of patients. Stratification of patients who have extragastrointestinal stromal tumor into those with 0 to 1 adverse histologic factors versus those with 2 to 3 offers the advantage of separating patients into two groups that have a markedly different risk for adverse outcome in the short term (0.02 events versus 0.54 events per person-year; P < .001, respectively).

Extragastrointestinal (soft tissue) stromal tumors are histologically and immunophenotypically similar to their gastrointestinal counterpart but have an aggressive course more akin to small intestinal than gastric stromal tumors.

Mod Pathol 2000;13:577-585.

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Last Updated 12/15/2003

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