الفهرس 
Pathology of Gastrointestinal Stromal TumorsOnly 14 pages are availabe for public view
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Abstract
Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor of the gastrointestinal tract. However, it only represents 1-2% of all neoplasms of the digestive tract. They were previously considered smooth muscle tumors as leiomyomas. The discovery that GIST arises from the interstitial cells of Cajal categorized this tumor as a separate entity from other mesenchymal tumors.
The median age of presentation is usually in the 60’s with an equal prevalence in both sexes. The most common site of affection is the stomach. Many patients present with clinical symptoms, others are discovered accidentally during an abdominal exploration or a radiological study for another purpose while others are only identified at autopsy. The most common symptom is gastrointestinal bleeding however, other vague abdominal symptoms may occur or symptoms of metastasis.
GISTs have a highly variable biological behavior, they are not usually classified as benign or malignant. Several factors determine the aggressiveness of the tumor, metastatic potential and the recurrence risk. These factors include size, location and mitotic rate. The usual site of metastasis is the liver. Lymph node metastasis is very rare.
Contrast enhanced computed tomography (CT) is the imaging modality of choice for the initial evaluation, staging and monitoring of treatment responses in GISTs. Endoscopic ultrasound is the most accurate and the preferred method of imaging for GISTs. Cytological tissue samples can be obtained through endoscopic ultrasound- fine needle aspiration.
The histological and more precisely the immuno-histochemical diagnosis remains the main stay for diagnosis. The identification of tyrosine kinase receptor with C-KIT (also referred as CD 117) as well as platelet derived growth factor alpha are essential for diagnosis. Many other immuno-histochemical stainings can assist the diagnosis and help to differentiate GISTs from other soft tissue tumors.
A multi-disciplinary team is necessary to evaluate the different modalities of treatment. Surgical resection remains the main stay treatment modality available. However, the problem arises when facing advanced, recurrent or metastatic GISTs. The revolutionary discovery of imatinb, a tyrosine kinase inhibitor has shown good results with GISTs. It can be used in the adjuvant setting of advanced and metastatic GISTs. It also can be used as a neo-adjuvent before resection of a locally advanced or a marginally resectable GIST.
Endoscopic resection for localized and small GIST represents the new era in the surgical treatment of GISTs. Endoscopic ultrasound hence can be used as a surveillance modality post resection. Laparoscopic surgeries are an option in treatment of GISTs, however only in experienced hands due to the fear of rupture of the tumor capsule, hence dissemination.
Response to treatment by the chemotherapy can be evaluated by CT and Positron Emission Tomography (PET), the latter owing to the high metabolic rate of the tumor.