[Histopathologic diagnosis of gastrointestinal stromal tumor (GIST)]

Gastrointestinal stromal tumor (GIST) as an ideal model for targeted therapy in recent years has been placed in the lime-light of oncology. Once thought to be a tumor of smooth muscle origin and formerly practically therapy resistant lesion is now justified to differentiate toward interstitial cells of Cajal; and crucial step of the development of this tumor is the gain-of-function mutation of c-kit gene localized to chromosome 4q11-21. Due to phenotypic variability of GISTs for reliable diagnosis, it is essential to perform c-kit (CD117) immunohistochemical reaction. The positive reaction not only supports the diagnosis, but also predicts efficiency of imatinib therapy. Differential diagnosis of GISTs includes, among others, the possibility of gastrointestinal leiomyomas, leiomyosarcomas, schwannomas, inflammatory fibroid polyps or GIST mimicking secondary tumors. When an abdominal lesion is suspicious for GIST, application of wider range of antibodies including c-kit (CD117), CD34, desmin, S100, alpha smooth-muscle actin is justified. The aim of this synopsis is to overview development of our knowledge about GIST and to discuss differential diagnostic problems. Basic molecular mechanisms responsible for development of GIST are also reviewed.