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.