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GIST Immunohistochemistry Diagnostic Markers
The standard diagnostic workup for GIST includes CD117 antibody-linked staining for the extracellular region of KIT. Nearly all GISTs are KIT (CD117) positive6. However, there is a range of staining intensity that may be related to tumour morphology. For example, cell membranes of epithelioid type tumours may be easier to observe than those in spindle-cell type tumours because of the narrow cross-dimension of the spindle cells28.
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Figure 2 GIST:Immunohistochemistry
KIT staining provides a primary point of distinction in differentiating GISTs from other GI nonepithelial neoplasms, including leiomyoma, leiomyosarcoma, and schwannomas. GISTs, unlike the others, typically stain strongly for KIT (CD117). Analysis of several other immunohistochemical markers is considered standard1,6,25:
- KIT tyrosine kinase receptor is positive in 95% of GISTs
- CD34, another transmembrane protein, is positive in about 60%-70% of GISTs
- Smooth muscle actin (SMA) is positive in up to 40% of GISTs
- Desmin is a protein typical of muscle cells and is rarely positive in GIST
- S-100 is a neural Schwann cell marker and is rarely positive in GISTs (5%)
GIST Molecular Analysis
For the minority of GIST cases that are not CD117 positive, the diagnosis should be referred to a pathologist who is experienced in diagnosing GIST. Of the 5% of histologically suspected GIST that are CD117 negative, molecular analysis for KIT and PDGFRA mutations should be considered6. In mutational analysis of the KIT and PDGFRA genes, about 35% of GISTs that stain negative for KIT may harbour mutations in the PDGFRA gene16.
Read about Treatment Options for GIST, including prognostic indicators, goals of therapy, and historical and current treatment options.