Gastrointestinal Stromal Tumors/Smooth Muscle Tumors (GISTs) Primary in the Omentum and Mesentery

Abstract

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.

Extragastrointestinal (Soft Tissue) Stromal Tumors: An Analysis of 48 Cases with Emphasis on Histologic Predictors of Outcome

“…As a group, they seem to resemble small intestinal stromal tumors more so than gastric ones. However, skeinoid fibers, a common marker of many small intestinal stromal tumors, was not encountered in any tumor in our group, although they were rarely noted in a previous study (13). Because precise localization of abdominal tumors (i.e., origin in omentum versus mesentery) was not possible in most cases, we cannot comment on site-specific histologic differences in EGIST as has been done with GIST.…”

“…There was also no correlation between the two histologic patterns noted in EGIST and outcome, although nonorganoid growth and a predominance of epithelioid areas have been associated with adverse outcome in the duodenum and jejunum/ileum, respectively. A recent study (13) of a small number of omental (nine cases) and mesenteric (seven cases) EGIST seemed to show a better prognosis for the former group. We are skeptical about accepting this statement at face value because of the extremely small sample size, short follow-up, and lack of stratification of these cases for other parameters that arguably affect outcome.…”

“…Over the past few years, it has become increasingly apparent that these tumors need to be studied on a sitespecific basis because of differences in behavior (2,9) and that malignancy is best described in terms of risk factors (10). Although numerous studies have addressed these issues in GIST (11)(12)(13)(14)(15)(16)(17)(18)(19)(20), there has been no study of those rare stromal tumors that develop outside the gastrointestinal tract in the soft tissues of the abdomen with respect to histologic features that predict outcome. A recent study compared a small number of omental and mesenteric GIST with respect to outcome but did not analyze various histologic parameters within these two groups (13).…”

“…Although numerous studies have addressed these issues in GIST (11)(12)(13)(14)(15)(16)(17)(18)(19)(20), there has been no study of those rare stromal tumors that develop outside the gastrointestinal tract in the soft tissues of the abdomen with respect to histologic features that predict outcome. A recent study compared a small number of omental and mesenteric GIST with respect to outcome but did not analyze various histologic parameters within these two groups (13). This study analyzes the clinicopathologic features of 48 such cases and evaluates a number of parameters to determine which most accurately predict adverse outcome.…”

Gastrointestinal Stromal Tumor Mimicking as Ovarian Tumor in Gynaecologic Oncology

“…Gastric lesions are characterized by a homogeneous enhancement, while small bowel lesions are more heterogeneous. Distal small bowel tumors and those arising from the sigmoid colon and rectum may be erroneously identified as gynecologic cancers [16][17][18][19][20]. Gross histopathologic findings typically include a fish-flesh appearance of soft consistency.…”