<unk>  was introduced as a diagnostic term in 1983. Until the late 1990s, many non-epithelial<unk> s of the<unk>  tract were called<unk> s". Histopathologists were unable to specifically distinguish between types we now know to be dissimilar molecularly. Subsequently, CD34, and later CD117 were identified as markers that could distinguish the various types. Additionally, in the absence of specific therapy, the diagnostic categorization had only a limited influence on prognosis and therapy. The understanding of<unk>  biology changed significantly with identification of the molecular basis of<unk> , particularly c-KIT. Historically, literature reviews prior to the molecular definition of<unk> , and for a short time thereafter, asserted that 70-80% of<unk> s were benign. The identification of a molecular basis for<unk>  led to the exclusion of many<unk> s that had been considered as<unk>  previously, and also the incorporation of a much larger number of<unk> s that had been labeled as other types of sarcomas and undifferentiated carcinomas. For example, some previous diagnoses of stomach and small bowel leiomyosarcomas (malignant<unk>  of smooth muscle) would be reclassified as<unk> s on the basis of immunohistochemical staining. All<unk><unk> s are now considered to have malignant potential, and no<unk><unk>  can be definitively classified as "benign". Hence, all<unk> s are eligible for cancer staging in the AJCC (7th edition) / UICC. Nonetheless, different<unk> s have different risk assessments of their tendency to recur or to metastasize, dependent on their site of origin, size, and number of mitotic figures. Due to the change in definition, clinical pathways of care before the year 2000 are largely uninformative in the current era.
Gastrointestinal stromal tumor
Ectopic pancreas
Krukenberg tumor
Signet ring cell carcinoma
Lipoblastoma
Nesidioblastoma
Angiomyofibroblastoma
Myxoid cyst