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Great Post... Another Great Big Book snipet: GISTs are usually located within wall of GI tract, usually stomach (particularly epithelioid variants). Less commonly esophagus, small bowel, and rectum. Rarely seen in the colon. Clinically range from asymptomatic to obstructed bowel. GISTs also occurs in rare syndrome of Carney's triad: (multinodular/multifocal epithelioid cell GIST, pulmonary chondroma, extra-adrenal paraganglioma).HISTOLOGY: Variable histologic appearance. Some are histologically identical to leiomyoma. Some have epithelioid features. Others have neural features (palisading of nuclei). SPECIAL STAINS/STUDIES: GISTs express CD117 (c-kit). In this context, IHC serves as a surgate for the activating mutations in c-kit that are commonly seen in GIST (>90%). Different mutations have different prognosis and response to imatinib (Debiec-Rychter M et al., Kit mutations and dose selection for imatinib in patients with advanced GIST. European Journal of Cancer. 2006; 42:1093-1103.) C-kit mutation negative GISTs often have activating mutations in PDGFR. BEHAVIOR: Major criteria for malignancy are size (greater than 5 cm) and mitotic rate. Other less predictive features are cellularity, and mucosal invasion. Risk of malignancy varies with location, esophagus or rectal origin are usually benign. Small bowel or deep rectum are usually malignant. Stomach GISTs have the least predictable clinical behavior. GISTs with exon 9 c-kit mutations generally have a worse prognosis than GISTs with exon 11 c-kit mutations. However, exon 9 mutation GISTs respond to imatinib dose escallation (leveling out prognosis). GISTs can develop imatinib resistance mutations analogous to BCR-ABL imatinib resistance mutations (Heinrich MC et al. Molecular Correlates of Imatinib resistance in GIST. JCO 2006; 24: 4764.)

----Comment by: PathDoc15 on 5/13/2009 5:58:45 AM


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