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| Gastrointestinal Stromal Tumor |
| Etiology •Unknown |
| Pathogenesis •Unknown •While it is difficult to distinguish between some benign mesenchymal tumors and low grade sarcomas, there is no convincing evidence that intestinal sarcomas arise from their beniogn counterparts. •While some tumors show evidence of clearcut differentiation, most commonly smooth muscle, many show evidence of of two or more differentiated cell lines prompting the current practise to call these tumors "Gastointestinal Stromal Tumors"(GIST) and then specifiy the particular line of differentiation identifies. •The adoption of GIST also suggests that these tumors may arise from a multipotential progenitor cell., |
| Epidemiology •Incidence increases between age 30-60yrs. and then levels off. •Equal incidence in men and women, although some series report a female predominance. •No geographic preference •Represent 20% of benign and malignant neoplasms of the small bowel. |
| General Gross Description •Malignant GIST tumors showing leiomyomatous differentiation most commonly present in the muscular wall of the jejeunum and ileum, and much less commonly in the large intestine. •The tumors are generally well circumscribed, with a white firm cut surface. •Large tumors may show central necrosis and hemorrhage. •Some tumors may be endophytic, bulging into the lumen of the intestine. •Smaller tumors have an intact overlying mucosal surface. •Many tumors are exophytic and bulge from the serosal surface into the peritoneal cavity or adjoining tissue. •Regional lymph nodes are usually unimpressive, as only 15% contain metastatic tumor. •Adjoining peritoneal surfaces and the liver are the most likely sites of metastatic tumor. |
| General Microscopic Description •Malignant GIST tumors usually have a spindle cell histology. •The most reliable parameter for a diagnosis of malignancy apart from the demonstration of metastases is mitotic rate. •All GIST tumors with >5 mitoses/10hpf should be considered to be malignant. •All GIST tumors with 1-4 mitoses/10hpf may have malignant potential as 40% of these tumors will eventually demonstrate metastases. •Tumors over 4cm in diameter should be considered to have malignant potential although this is a less reliable guide than mitotic activity. •The most reliable way to subclassify these tumors is the presence of specific markers on immunoperoxidase examination: Smooth Muscle -, Vimentin +, Actin +,Desmin +; Fibroblastic-Vimentin +; Neural-S-100 +, Vimentin +, and Neurofilament +; vascular-CD-34 + or Factor 8 + •Electrom Microscopy is a useful adjunct to identify specific cell organelles. |
| Clinical Correlation •Many GIST tumors when smaller are asymptomatic or have vague non localizing abdominal symptoms. •Malignant GIST tumors which are endophytic may present with evidence of obstruction or bleeding. •Exophytic tumors present as a large mass lesion or if perforation has occurred with evidence of peritonitis. •The only effective therapy is surgical removal, and the long term survival is 50% at best. •Chemotherapy and radiotherapy do not increase the salvage rate. •Only 15% of malignant GIST tumors involve regional nodes, with peritoneum, liver and lungs being the site of spread. |
| References •Cancer: Priciples and Practice of Oncology, 4th ed. DeVita VT et al (eds). Philadelphia, JB Lippincott, 1993, pp 915-928 •Gastrointestinal Pathology, Fenoglio-Preiser CM, etal. (ed) New York: Raven Press, 1989 pp 543-585 |
| Gastrointestinal Stromal Tumor |
| Synopsis by: Martin Nadel M.D. (T64000M88903)[488] |
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