Mesenchymal tumors
Gastrointestinal stromal tumor

Topic Completed: 1 October 2016

Minor changes: 1 October 2020

Copyright: 2002-2021,, Inc.

PubMed Search: Gastrointestinal stromal tumor [title] colon

Raul S. Gonzalez, M.D.
Page views in 2020: 4,586
Page views in 2021 to date: 185
Cite this page: Gonzalez R. Gastrointestinal stromal tumor. website. Accessed January 16th, 2021.
Definition / general
  • Tumors that differentiate along lines of interstitial cells of Cajal, the gut's pacemaker cells (Mod Pathol 2003;16:366)
Essential features
  • Mesenchymal spindle cell neoplasm caused by KIT or PDFRGA mutations
  • Risk stratification is based on location, size and mitotic rate
  • Very rare in colon; rectal GISTs account for roughly 5% of all GISTs
Clinical features
Prognostic factors
  • Risk of disease progression for rectal GISTs depends on tumor size and mitotic rate (Semin Diagn Pathol 2006;23:70)
    • If mitotic rate is < 5 per 5 square mm, risk of progression is 0% (< 2 cm), 8.5%(> 2 to < 5 cm) or 57% (> 10 cm) (insufficient data for > 5 to < 10 cm)
    • If mitotic rate is > 5 per 5 square mm, risk of progression is 54% (< 2 cm), 52% (> 2 to < 5 cm) or 71% (> 10 cm) (insufficient data for > 5 to < 10 cm)
  • There is insufficient data for progression estimation in colonic GISTs
Case reports
  • Tyrosine kinase inhibitors, including imatinib mesylate (first line) and sunitinib malate
Gross description
  • Often large, bulky, intramural masses
  • Fish flesh or tannish brown parenchyma with hemorrhage, necrosis and cystic softening
Gross images

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Outer surface of colorectal GIST

Cut surface of colorectal GIST

Microscopic (histologic) description
  • Mesenchymal tumor usually centered in the muscularis propria
  • Spindle cell GISTs: intersecting fascicles of plump spindled cells with eosinophilic cytoplasm within variably hyalinized or edematous stroma
  • Epithelioid GISTs: rounded epithelioid cells with pseudo compartmental organization
  • Skeinoid fibers (extracellular collagen globules) may be seen
  • Muscle infiltration is common but not predictive of behavior
  • Rarely has osteoclast-like giant cells (Arch Pathol Lab Med 2004;128:440)
Microscopic (histologic) images

Contributed by Raul S. Gonzalez, M.D.

Rectal GIST: low power

Rectal GIST: intermediate power

Rectal GIST: high power

Case #428

Focal proliferation of bland spindle cells with an irregular border located in the muscularis propria and extending into the pericolorectal soft tissue


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Epithelioid type of GIST

Spindled cells




Positive stains
Negative stains
Electron microscopy description
  • Processes or cell bodies with intermediate filaments showing solitary focal densities
  • Attachment plaques with incomplete lamina, rare myofilaments and smooth endoplasmic reticulum (Ultrastruct Pathol 2002;26:269)
Molecular / cytogenetics description
  • 80% have mutations in KIT, which encodes CD117; exons affected include 11, 9, 13 and 17 (Nat Rev Cancer 2011;11:865)
  • 10% have mutations in PDGFRA; exons affected include 18, 14 and 12; these GISTs are often gastric and epithelioid
  • Both mutations have been identified in small incidental GISTs, affirming their importance
  • Up to 10% have neither mutation and are associated with syndromes such as neurofibromatosis type 1 and Carney's triad
Differential diagnosis
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