Gastrointestinal stromal tumours

Gastrointestinal stromal tumour (GIST) is the designation used here to iden tify the most common subset of gastrointestinal mesenchymal tumours specifi c to those sites. These tumours have unique histological, imunophenotypic a nd molecular genetic features that set them apart from typical smooth muscl e tumours and schwannomas; however, by tradition, they have been classified as GI-smooth muscle tumours, or stromal tumours/smooth muscle tumours. GIS Ts occur predominantly in persons over 40 years of age with an equal sex in cidence. Benign GISTs outnumber the malignant ones by a margin of 10:1. GIS Ts occur throughout the gastrointestinal tract, but are most common in the stomach (60-70%) and small intestine (30%). GISTs are rare in esophagus, co lon and rectum. Histologically they may show a spindle cell or epithelioid pattern (the former largely corresponds with the designation of cellular le iomyoma and the latter with that of leiomyoblastoma). Immunohistochemically most GISTs are positive for CD34 and c-kit protein (CD117); the latter is quite specific for GISTs among mesenchymal tumours. Genetically GISTs commo nly show DNA losses in the long arm of chromosome 14, and c-kit gene mutati ons occur at least in some cases. c-kit is also expressed in the interstiti al cells of Cajal, the gastrointestinal pacemaker cells, and relationship o f GISTs to these cells has been proposed recently. GISTs differ histologica lly, imunohistochemically and genetically from typical (esophageal) leiomyo mas that are negative for c-kit and CD34 and neither show DNA-losses in 14q nor c-kit mutations. Evaluation of malignancy of GISTs is based on mitotic count, tumour size and extra-gastrointestinal spread. Tumours with mitotic counts higher than 5/10 high power fields or larger than 10 cm have a sign ificant risk for recurrence and metastasis and are considered histologicall y malignant; however, some tumours with mitotic activity <1/10HPF may metas tasize indicating some uncertainty in malignant potential of GISTs, especia lly those larger than 5 cm.