OBJECTIVETo investigate the morphological features, immunohistochemical speciality of the gastrointestinal stromal tumors (GISTs), and its histogenesis as well.

METHODSThe morphologic characteristics of GISTs were studied in 65 cases using light microscopy and 17 cases by electron microscopy. The expression of c-kit (CD117), CD34, vimentin, SMA, actin, desmin, S-100 and MBP were detected in all the cases with EnVision trade mark staining.

RESULTSAmong 65 cases of GISTs, 46 were spindle cell type, 6 epithelioid cell type and 13 mixture type, equivalent to 85.5% (65 of 76) of all of the mesenchymal tumors of gastrointestinal tract admitted in the same period. The epithelioid cell type tumors composed of mainly the epithelioid cells, predominantly short spindle, oval or round in pattern, with an overall eosinophilic cytoplasm by hematoxylin-eosin stain. Focal cytoplasmic vacuolization was often seen. Sometimes signet-ring like cells and cells with a clear cytoplasm were seen in the epithelioid stromal tumor. The tumor cells arranged in interlacing fascicles forming whorls or sometimes cell clusters. Electronic microscopy showed the presence of interdigitating cell processes, in some areas, synapse-like structure and numerous desmosome-like junctions as well as a few gap junctions and small round neurosecretory granules. There were also abundant intermediate filaments and thin filaments of actin-type with longitudinal condensations (dense bodies). All of the 65 stromal tumors were strongly positive for vimentin (100%), 61 out of 65 tumors positive for CD117 (c-kit) (93.8%) and 51 out of 65 positive for CD34 (78.5%). Some cases also expressed SMA, actin, S-100 and MBP.

CONCLUSIONSGISTs were the most frequent mesenchymal tumor seen in the gastrointestinal tract. Under light microscope, the morphology of stromal tumors looks sometimes like a leiomyoma and Schwannoma. The application of immunohistochemical markers (particularly CD117 and CD34) and ultrastructural study are considered necessary for the differential diagnosis. GISTs may originate from the pluripotential precursor cells like the interstitial cells of Cajal.