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What Pathologists Need To Know

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A Summary of Diagnostic and Prognostic
Features of GIST

Histological features
GISTs typically show 1 of 3 histologic patterns:
  • Predominantly spindle cells, arranged in short fascicles or whorls (Figure 1)
  • Predominantly epithelioid cells, in diffuse or nested architecture (Figure 2)
  • Mixture of spindle and epithelioid cells1
Figure 1

Spindle Cell GIST
Spindle Cell GIST
GIST comprised of
spindle cells
Figure 2

Epithelioid GIST
Epithelioid GIST
GIST comprised
predominantly
of epithelioid cells

Cytological features

Most GISTs exhibit uniform cytology, with fibrillary eosinophilic cytoplasm and nuclei containing fine chromatin and inconspicuous nucleoli.

Prominent paranuclear vacuoles, hyaline eosinophilic cytoplasmic structures (called skeinoid fibers), and extensive nuclear pallisading are seen in a few cases.

Significant cytologic pleomorphism is rare and could signal an alternative diagnosis1


Immunohistochemical Features

Histopathological assessment is perhaps the most important facet of GIST diagnosis.2

Histopathologic Features of GIST1
Common in GIST
Less Common in GIST
  • 95% are positive for KIT (CD117) (diffusively
    positive but nonuniform staining)
  • 60% to 70% are positive
    for CD34 (diffuse or local
    staining)
  • 30% to 40% are positive for smooth muscle actin (diffuse or local staining)
  • 5% are positive for S-100
  • 1% to 2% are positive for desmin
  • 1% to 2% are positive for keratin

Prognostic Features

Tumor size, mitotic index, and tumor site are 3 key prognostic features used to assess risk of GIST recurrence and ensure that patients who may benefit from adjuvant therapy are not excluded.1 The National Comprehensive Cancer Network consensus risk stratification, based on 3 large retrospective studies, is shown below:

Current NCCN criteria for risk stratification are based on tumor size, mitotic rate, and site1
Rate of Metastases or Tumor-Related Death in GIST3,a
Tumor Size (cm)
Mitotic Index (HPF)
Gastric
GIST
Jejunal and Ileal GIST
Duodenal
GIST
Rectal
GIST
≤2
>2 ≤ 5
>5 ≤ 10
> 10
≤5 / 50
0%
1.9%
3.6%
12%
0%
4.3%
24%
52%
0%
8.3%
34%b
0%
8.5%
57%b
≤2
>2 ≤ 5
>5 ≤ 10
> 10
>5 / 50
0%b
16%
55%
86%
50%b
73%
85%
90%
N/A%c
50%
86%b
54%
52%
71%b
HPFs, high power fields. Adopted from Miettinen and Lasota, 2006.
  • a Based on previously published long-term follow-up studies on 1055 gastric, 629 small intestinal, 144 duodenal and 111 rectal GISTs.
  • b Denotes tumor categories with very small numbers of cases. Some data combined, or missing, due to a small number of cases.
  • c No tumors of such category were included in the study. Note that small intestinal and other intestinal GISTs show are markedly worse prognosis in many mitosis and size categories than gastric GISTs.
Additional factors to be considered:4
  • Tumor rupture
  • Mucosal invasion
  • Mutational Status
Differences in evaluating mitotic index may have a dramatic impact on risk of progressive disease.3
 
  1. Demetri GD, Benjamin RS, Blanke CD, et al. NCCN task force report: management of patients with gastrointestinal stromal tumor (GIST)—update of the NCCN clinical practice guidelines. J Natl Compr Canc Netw. 2007;5(suppl 2):S1–S29.
  2. Eisenberg BL, Judson I. Surgery and imatinib in the management of GIST: Emerging Approaches to adjuvant and neoadjuvant therapy. Ann Surg Oncol. 2004;11(5):465-475.
  3. Miettinen M, Lasota J. Gastrointestinal stromal tumors: pathology and prognosis at different sites. Semin Diagn Pathol. 2006:23(2):70-83.
  4. Joensuu H. Risk Stratification of patients diagnosed with gastrointestinal stromal tumor. Hum Pathol. 2008:39(10); 1411-1419.
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