Appendix

• Gastrointestinal stromal tumor arising in the appendix, analogous to those from other digestive sites

• Very rare, with only four cases at AFIP during 1970 - 1998 (Am J Surg Pathol 2001 ;25:1433)
• Seemingly M > F
• Mean age roughly 65 years

• 7 year old boy with appendix GIST (Pediatr Surg Int 2014;30:457)
• 56 year old man with appendiceal hemorrhage (World J Gastroenterol 2007;13:3265)
• 67 year old man with 22 cm appendix mass (Mol Clin Oncol 2017;7:399)
• 68 year old man with cystic appendix mass (Int J Surg Case Rep;21:20)
• 75 year old man with acute appendicitis (Hum Pathol 2013;44:651)

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Contributed by Raul S. Gonzalez, M.D.


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Which of the following is true about GISTs of the appendix?

1. Likely more common in men
2. Negative for DOG1 by immunohistochemistry
3. Often large with abundant mitotic activity
4. Typically have PDGFRA mutations

A. Likely more common in men

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Reference: Gastrointestinal stromal tumor

This mesenchymal tumor was found incidentally within an appendix removed for appendicitis. What immunohistochemical stains would most likely be positive in this tumor?

1. CD117 and DOG1
2. Desmin and SMA
3. S100
4. Synaptophysin and chromogranin

A. CD117 and DOG1. This lesion is a gastrointestinal stromal tumor (GIST), as evidenced by the bland spindled cells, perinuclear vacuoles and skeinoid fibers. The appendix is a rare location but as with GISTs elsewhere in the gastrointestinal tract, they are positive for CD117 and DOG1 by immunohistochemistry.

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Reference: Gastrointestinal stromal tumor