Patterns of nestin and other intermediate filament expression distinguish between gastrointestinal stromal tumors, leiomyomas and schwannomas

The KIT-positive specific gastrointestinal stromal tumors (GISTs), leiomyomas, and schwannomas are the three most common types of primary mesenchymal tumors of the gastrointestinal (GI) tract. The intermediate filaments are abundant cytoskeletal proteins commonly used as cell differentiation markers in diagnostic immunohistochemistry. Their patterns have not been fully characterized in GI mesenchymal tumors, and could offer differential diagnostically useful parameters. Very recently, nestin, a class VI intermediate filament expressed in neuroectodermal stem cells and skeletal muscle progenitor cells, has been shown in GISTs and suggested as a marker for these tumors. In this study we immunohistochemically examined the expression of nestin and other intermediate filament proteins, including desmin, keratins (Ks), glial fibrillary acidic protein (GFAP), neurofilament, and vimentin in GISTs of different sites, esophageal leiomyomas and GI schwannomas. Nestin was nearly consistently present in GISTs of different locations whether spindle cell or epithelioid, and benign or malignant. It was also detected in 23 of 24 (96%) GI schwannomas, whereas leiomyomas were uniformly negative. Vimentin was present in both GISTs and schwannomas, whereas it was typically absent in leiomyomas (25% positive, usually focally). Desmin was present in all leiomyomas, whereas only 3% of GISTs (4 of 140) were positive, and all schwannomas were negative. K18 was detected in a minority of GISTs, leiomyomas, and schwannomas. Malignant GISTs were more commonly keratin positive than the benign ones; there was 18% K18 positivity in malignant gastric and small intestinal GISTs, but 9% K18 positivity in benign gastric and small intestinal GISTs. Moreover, K8, albeit to a lesser degree, was detected in a minority of GISTs, but K7, K14, K19 and K20 were not detected. GFAP was present in the majority of schwannomas, whereas all GISTs were negative; some leiomyomas had, weak cytoplasmic positivity. These results document distinctive patterns of intermediate filament proteins in GI mesenchymal tumors. Nestin is confirmed to be consistently expressed in GISTs but it is also present in most GI schwannomas; GFAP is helpful when separating GISTs and schwannomas, since only the latter are positive. The potential presence of K8 and K18 in GISTs should not lead to the misdiagnosis of carcinoma on biopsy.