الفهرس 
Histology of the Gastrointestinal TractOnly 14 pages are availabe for public view
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Abstract
G
ISTs are rare, however, they are the most common mesenchymal tumors of the GI tract.These can arise anywhere in the gastrointestinal tract (from the esophagus to the rectum), with the majority arising in the stomach or small intestine, and infrequently in the esophagus, mesentery, omentum, colon, or rectum.
GISTs are now widely believed to originate from, or to be closely related to, the interstitial cells of Cajal (ICC).Which play an important role in pacemaker activity and motility of the GI tract.
In general, extremely bulging tumors are more common than intraluminal masses.Focal mucosal ulceration is common in GISTs of all sites, and is not related to tumor malignancy.
The predominant histologic pattern, seen in 70-80% of GISTs, is of a spindle cell tumor with a fascicular or storiform growth pattern.
KIT or PDGFRα mutations, with mutually exclusive pattern, occur early in the pathogenesis of GIST, as they are found even in very small tumors. Progression of GIST has been shown to be related to various chromosomal aberrations.
In a minority of cases (10-15%) no mutations in the known KIT or PDGFRαA hot spots are detected although these tumors express the KIT protein. This subgroup is called wild type GIST (wt-GIST) and comprises tumors in pediatric patients, in patients affected by the Carney triad, neurofibromatosis type 1 (NF1) associated GIST and a subset of sporadic adult GIST.
GISTs must be distinguished from smooth muscle tumors, nerve sheath tumors, and fibromatosis.In immunohistochemistry, 90% to 95% of GISTs will be diffusely and strongly positive for CD117 (c-Kit). D34 is positive in 60% to 70% of GISTs, where as S100 protein stains up to 5% of these tumors. Smooth muscle actin (SMA) is expressed in 30% to 40% of the cases, and 1%to 2% of cases are positive for desmin. h-Caldesmon is positive in 85% of GISTs and may be useful to support the diagnosis in CD117 negative tumors.
Small tumors may be asymptomatic and GISTs can grow to a large size before producing any symptoms. This may be because GISTs grow by displacing adjacent structures rather than invading them.Presenting symptoms can therefore include non-specific GI symptoms such as nausea, vomiting, dyspepsia, abdominal pain, distension, or change in bowel behavior. Symptomatic esophageal GISTs usually present with dysphagia or as a mediastinal tumor.Symptomatic gastric and small bowel GISTs usually present with nonspecific complaints such as early satiety and bloating. Occasionally they can ulcerate and bleed, or grow large enough to cause pain or obstruction.The most common sites of metastases are the peritoneum and liver, whereas lymph node metastases are relatively rare.
Computerized Tomography (CT) is the imaging modality of choice for the evaluation, staging and monitoring of treatment response in GISTs.
Surgery is the standard initial management for all localized GISTs. Imatinib (Gleevec) is used for treatment of unresectable and metastatic GIST, as well as for prevention of recurrence of higher-risk GISTs (adjuvant therapy). Sunitinib (Sutent) is used for treatment of GIST resistant to imatinib and for patients who are intolerant of imatinib.There are also alternate Tyrosine Kinase Inhibitors and Novel therapeutic drugs which are still in pre-clinical development and in clinical trials.Hepatic artery embolization may provide palliation in patients with GIST metastatic to the liver.
Conclusion:
• CT is the investigation of choice for GIST evaluation staging monitoring and treatment.
• Localized GISTs are treated by surgical removal.
• Imatinib is the drug of choice for unresectable and metastatic GISTS and also as adjuvant therapy.
• There are other alternate tyrosine kinase inhibitors and novel therapeutic drugs.