| [ Summary ] |
Although the term gastrointestinal stromal tumors (GIST) has been in widespread use recently, it remains problematic with regard to the origin, differentiation and nomenclature of various lesions. GIST has been used to designate histologically neutral mesenchymal tumors, which have neither neurogenic nor smooth muscle origin. On the other hand, the term gastrointestinal mesenchymal tumor (GIMT) includes most of those tumors previously designated as leiomyoma, epithelioid leiomyoma (leiomyoblastoma) and schwannoma. Histologically, GISTs appear as spindle, epithelioid or palisading cells. A significant percentage of GISTs also demonstrate a malignant character, resulting in distant metastasis. Predicting the malignancy of GISTs, however, is often difficult. The most reliable criteria for the malignant distinction is a tumor greater than or equal to 5cm in size with a mitotic rate of 5/50 HPF (high power field) or more. Immunohistochemically, most GISTs are positive for CD117 (c-kit), and recent studies indicate that many display activating mutations in the c-kit gene. Recent findings also suggest that GISTs originate from the interstitial cells of Cajal. The term gastro intestinal autonomic nerve tumor (GANT) has also been used to describe tumors designated as "plexosar comas" based on ultrastructural findings that show a synapse like structure with dense core granules. However, in the current study, GANTs and GISTs overlap due to the fact that GANTs also show a positive reactivity for the c-kit receptor, representing a differ entiation of Cajal cells. In conclusion, GISTs differ from true leiomyomas and schwannomas due to their diffuse positivity for the c-kit receptor, and therefore constitute the majority of all GIMTs. |