Gastrointestinal Stromal Tumors in Equids

Abstract

Abstract. Eleven gastrointestinal neoplasms from 10 aged horses and 1 pony were examined grossly, histologically, immunohistochemically, and (in two cases) ultrastructurally. Clinical signs were associated with two neoplasms, and the other nine tumors were incidental findings at laparotomy or necropsy. The neoplasms were solitary (9/11) or multifocal (2/11), well demarcated, serosal or mural masses of stomach (1), jejunum (1), ileum (3), cecum (5), and/or colon (2). Microscopic examination revealed discrete spindle cells arranged in compact patterns with fascicles and whorls or cribriform pattern with fascicles and rare palisades, often with a myxoid interstitial matrix. Three tumors infiltrated between the muscularis interna and the muscularis externa at the myenteric plexi. All neoplasms were vimentin positive, 3/11 were S-100 positive, 2/11 were muscle actin positive, and no neoplasm was positive for glial fibrillary acid protein, desmin, factor VIII, chromogranin, or neuron-specific enolase. Of the two tumors studied ultrastructurally, one contained an admixture of smooth muscle cells and cells resembling Schwann cells, and the second was populated by homogeneous fusiform mesenchymal cells separated by homogeneous matrix. Gastrointestinal stromal tumors (GIST) have been recognized in humans, more recently in dogs and nonhuman primates, and now in equids. Most of these tumors are comprised of a loosely arranged network of spindled cells separated by myxoid matrix. GIST may be composed of myogenic, neurogenic, combined myogenic and neurogenic, and undifferentiated mesenchymal cells.

An Atypical Equine Gastrointestinal Stromal Tumor

“…3 The mass was attached to the transverse colon by a vascular peduncle, which is somewhat similar to a previously reported equine case. 3 Although the cecum and ileum 3,6 are the most commonly reported sites for this neoplasm, equine GISTs also have rarely been reported in the large colon, 3 as in the current case. In this horse, as in a small number of other cases, there were associated clinical signs.…”

“…Akin to the majority of other equine cases, the mass in the current study occurred as a solitary, well-demarcated, moderately soft, tan, cribrous mass 3,6 in a mature horse. 3 The mass was attached to the transverse colon by a vascular peduncle, which is somewhat similar to a previously reported equine case.…”

“…[6][7][8]11,12 Because the interstitial cells of Cajal (ICCs), which differentiate into the pacemaker cells of the intestinal tract, have a similar immunophenotype, ICCs are hypothesized by many to be the progenitor cells of GISTs. 2,3,[6][7][8]11 Neoplasms with many analogous features have been reported in nonhuman primates, 1,15 dogs, 4,9,10 horses, 3,6 and most recently in a Fischer 344 rat. 5 The current case report describes an atypical equine GIST with several unique features.…”

“…3,13,14 Because the histogenesis of these neoplasms remains unclear, the term gastrointestinal stromal tumor (GIST) is often applied. 2,3,6,11,12,14 The majority of human GISTs express cluster of differentiation (CD)117, and a slightly smaller number are also positive for CD34.…”

Three Cases of Canine Gastrointestinal Stromal Tumors with Multiple Differentiations and c-kit-Expression

“…Human GISTs are reported to arise in the esophagus, anus, and even omentum, mesen-and retro-peritoneum besides the gastrointestinal wall [9,17,23]. In animals, tumors resembling to human GISTs have been reported in rhesus macaques [1], dogs [10], and horses [2,3]. The present study describes morphological, immunohistochemical, and ultrastructural features of GISTs with c-kit expression in 3 dogs.…”