Mesenchymal tumors

Gastrointestinal stromal tumor

Last author update: 24 February 2021
Last staff update: 10 March 2021

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PubMed Search: Gastrointestinal stromal tumor[TI] free full text[sb] colon

Raul S. Gonzalez, M.D.
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Cite this page: Gonzalez RS. Gastrointestinal stromal tumor. website. Accessed June 2nd, 2023.
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
  • Leiomyoblastoma and gastrintestinal autonomic nerve tumor (GANT) are old terms no longer used
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
  • Man in mid 40s with GIST of the transverse colon
  • 65 year old man with prostatic stromal sarcoma and rectal GIST (Urology 2006;68:672.e11)
  • 71 year old man with a large rectal adenoma and interstitial cell of Cajal hyperplasia (Case #428)
  • 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

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Epithelioid cells and osteoclast-like giant cells

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
Sample pathology report
  • Ascending colon, resection:
    • Gastrointestinal stromal tumor (4.3 cm) (see synoptic report and comment)
    • Comment: The tumor is positive for KIT and DOG1 by immunohistochemistry. The mitotic rate is 2 per 5 square mm. Risk stratification for colonic GISTs has not been established but the risk in this case is likely relatively low (an analogous rectal GIST would have a risk of progression of 8.5%).
Differential diagnosis
Board review style question #1
What is the most common site for gastrointestinal stromal tumors in the large intestine?

  1. Appendix
  2. Cecum
  3. Rectum
  4. Transverse colon
Board review style answer #1
Board review style question #2
What 2 factors are used to estimate risk of progression in gastrointestinal stromal tumors?

  1. Ki67 index and necrosis
  2. Ki67 index and size
  3. Mitotic rate and necrosis
  4. Mitotic rate and size
Board review style answer #2
D. Mitotic rate and size

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Reference: Gastrointestinal stromal tumor
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