Which immunohistochemical marker is characteristic of GIST?

Which immunohistochemical marker is characteristic of GIST?

• A. CD20
• B. CD117 (c-KIT)
• C. Chromogranin A
• D. CK7

Answer: (B)

GISTs arise from interstitial cells of Cajal and are classically driven by activating mutations in KIT, the receptor tyrosine kinase. Immunohistochemically, this is most characteristically seen as strong membranous staining for CD117, reflecting KIT expression on the tumor cells. This marker is what helps distinguish GIST from other mesenchymal tumors in the GI tract, such as leiomyomas (which tend to express desmin and smooth muscle actin) or schwannomas (which are S-100 positive). While another marker, DOG1, is also commonly positive in GISTs, the classic teaching centers on CD117 positivity. The other options—CD20 (a B-cell marker), Chromogranin A (a neuroendocrine marker), and CK7 (an epithelial marker)—do not characterize GISTs and point to other lineages if positive.

GISTs arise from interstitial cells of Cajal and are classically driven by activating mutations in KIT, the receptor tyrosine kinase. Immunohistochemically, this is most characteristically seen as strong membranous staining for CD117, reflecting KIT expression on the tumor cells. This marker is what helps distinguish GIST from other mesenchymal tumors in the GI tract, such as leiomyomas (which tend to express desmin and smooth muscle actin) or schwannomas (which are S-100 positive). While another marker, DOG1, is also commonly positive in GISTs, the classic teaching centers on CD117 positivity. The other options—CD20 (a B-cell marker), Chromogranin A (a neuroendocrine marker), and CK7 (an epithelial marker)—do not characterize GISTs and point to other lineages if positive.