Appendix
Other tumors
Gastrointestinal stromal tumors (GIST)

Editor-in-Chief: Debra Zynger, M.D.
Raul S. Gonzalez, M.D.

Topic Completed: 3 January 2019

Revised: 3 January 2019

Copyright: (c) 2003-2019, PathologyOutlines.com, Inc.

PubMed Search: Gastrointestinal stromal tumor appendix


Raul S. Gonzalez, M.D.
Page views in 2018: 337
Page views in 2019 to date: 575
Cite this page: Gonzalez R. Gastrointestinal stromal tumors (GIST). PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/appendixGIST.html. Accessed July 18th, 2019.
Definition / general
  • Gastrointestinal stromal tumor arising in the appendix, analogous to those from other digestive sites
Essential features
  • Extremely rare location for gastrointestinal tumor (GIST)
  • Almost always incidental / small and indolent
  • Harbors KIT mutations, as do most GISTs elsewhere
ICD coding
  • ICD-10: C49.A0 - gastrointestinal stromal tumor, unspecified site
Epidemiology
Clinical features
  • May be incidental or associated with appendicitis-like symptoms
  • Nearly all cases appear to follow indolent course, though aggressive behavior (invasion and perforation of adjacent bowel) has been reported (J Gastrointest Cancer 2010;41:9)
Prognostic factors
  • Presumably size and mitotic rate, as for other GISTs but no large case series has validated this for the appendix
Case reports
Treatment
  • Surgery
  • Responds to imatinib if necessary
Gross description
  • Firm nodule (usually small) expanding and potentially obliterating appendiceal wall
Gross images

Images hosted on other servers:

Small GIST of appendix

Pedunculated cystic GIST

Pedunculated GIST after imatinib

Microscopic (histologic) description
  • Resemble GISTs at other sites
  • Bland eosinophilic spindle cell tumor, often with extracellular collagen globules (skeinoid fibers)
  • Generally no atypia and little / no mitotic activity
  • May be well circumscribed
  • Artifactual perinuclear vacuoles may be seen
Microscopic (histologic) images

Contributed by Raul S. Gonzalez, M.D.

Well circumscribed tumor

Bland spindle cells



Images hosted on other servers:

Small appendiceal GIST

Bland appendix GIST

Positive stains
Negative stains
Molecular / cytogenetics description
Differential diagnosis
Board review question #1
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
Board review answer #1
A. Likely more common in men

Comment here
Board review question #2
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
Board review answer #2
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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