[Histology and molecular biology of GIST]

Gastrointestinal stromal tumors (GIST) are the most frequent sarcomas but were underdiagnosed until the beginning of this century. GIST derive from interstitial cells of Cajal and may develop all along the digestive tract. GIST are characterized by the expression of KIT (CD117), and also DOG-1, which was recently discovered by transcriptome analysis. Gain-of-function mutations of the tyrosine kinase receptors KIT and PDGFRA are present in 85% of cases. More than 150 different mutations have been reported, mostly located in exon 11 of the KIT gene. Detection of these mutations may be useful to confirm the diagnosis and to evaluate the prognosis. Mutations also have predictive value. For example, patients with metastatic GIST and a duplication of KIT exon 9 should receive twice the usual dose of imatinib, while GIST with the PDGFRA p. D842 V mutation are resistant to imatinib. This article presents the main pathologic characteristics of GIST and the important insights that GIST research has provided for oncology in general.