[GIST: definition, physiopathology].

: Gastrointestinal stromal tumors (GIST) are the most frequent mesenchymal tumours of the digestive tract. They can arise anywhere in the gastrointestinal tract, from oesophagus to anus, and rarely from peritoneal cavity or mesentery. GIST usually remain asymptomatic for a long time. Therefore 10 to 20% are found incidentally at endoscopy or at time of surgery for others reasons and metastases are found in 15 to 50% of cases at diagnonis. Histologicaly, they are characterized by a cellular proliferation constituted of either spindle or epithelioid cells. Diagnosis has to be confirmed by immunohistochemistry, with positivity of KIT in 95% of cases, or by molecular biology, with "gain of function" mutations of KIT or PDGFRA in 85% of cases. Primary localization, mitotic activity and tumor size are the main prognostic factors. Metastases occur in 30 to 50% of patients with GIST. GIST are highly resistant to conventional chemotherapy and results obtained with new targeted therapies like Imatinib constitute one of the major progress in oncology during the decade.