Role of PET/CT in Gastrointestinal Stromal Tumors

Document Type : Editorial

Author

Nuclear Medicine, Faculty of Medicine, Cairo University, NCI, Cairo, Egypt.

Abstract

The first accurate description of mesenchymal neoplasms of the gastrointestinal tract (GIT) was in 1941. With the advent of immuno-histochemical analysis a definition of a new entity among gastrointestinal mesenchymal tumors called the gastrointestinal stromal tumors (GISTs); which particularly express the kit (CD117) protein; a growth factor trans-membrane receptor with tyrosine kinase activity(1 ) . Gastrointestinal stromal tumors (GISTs) are the most frequent mesenchymal tumors of the gastrointestinal tract(2). GISTs are usually found in the stomach or small intestine but can occur anywhere along the gastrointestinal tract and rarely have extra-gastrointestinal involvement. Approximately 50-70% of GISTs originate in the stomach. The small intestine is the second most common location, with 20-30% of GISTs arising from the jejuno-ileum. Less frequent sites of occurrence include the colon and rectum (5-15%) and esophagus (<5%). Primary pancreatic, omental, or mesenteric GISTs have been reported but are very rare (3). Surgery remains the mainstay of therapy for patients with primary GIST who do not have evidence of metastasis and should be the initial therapy if the tumor is technically resectable with acceptable risk of morbidity. Regarding patients with a positive microscopic margin on final pathologic analysis, the management is still not well defined. There is no evidence that those patients with complete resection of all macroscopic disease, but still have microscopically positive margins, need to undergo re-excision. Lymphadenectomy is usually unnecessary because lymph node metastases are rare with GIST and sarcomas in general (4). There are different schemes for classification of GISTs on the basis of tumor size and mitotic count into very low risk, low risk, intermediate risk, and high risk. Alternatively, they are classified according to site, size, and mitotic activity into 3 categories: benign, malignant, and uncertain or low malignant potential. Gastrointestinal stromal tumors are subclassified according to their cellular pattern into spindle, epithelioid, and mixed patterns. A final consensus on GISTs classification has not been achieved, and the biologic behavior is often uncertain. Whether borderline GISTs are precursors of malignant GISTs that accumulate genetic alteration during malignant transformation or whether they represent a biologically indolent and distinct subset of GISTs is still uncertain(5).

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