Tissue Tumour Online
Pathology of Gastrointestinal
Stromal Tumour (GIST)
stromal tumours (GIST):
These are mesenchymal tumours arising in the Gastrointestinal tract and sometimes within the abdomen without gastro-intestinal connection.
Recent studies indicate that the tumour shows differentiation towards interstitial cells of Cajal.
( Interstitial cells of Cajal link the autonomic innervation of the gut with smooth muscle cells and regulate Gastrointestinal motility ).
2) Common in adults aged 50-60 years:
Presents as a primary tumour or metastatic mass.
25% of GISTs are malignant.
May be associated with von Recklinghausen's disease and Carney's triad (epitheliod gastric stromal tumour , extradrenal paraganglioma and pulmonary chordoma)
Small intestine- 25-40%
Colorectal- Less than 10%
Omentum, peritoneum, retroperitoneum- about 7%
3) Macroscopic features:
Size vary between 1 to more than 20cm.
Submucosal, intramuscular or subserosal mass.
Usually well circumscribed but lack a true capsule.
Cut surface gray to pink in colour.
Areas of cystic degeneration, infarction and hemorrhage and necrosis.
Prone to surface ulceration and bleeding.
An hourglass defect may occur at the pylorus or cardia if the tumour encircles the stomach.
4) Microscopic features:
Short. uniform, blunt ended, eosinophilic cytoplasm. Paranuclear vacuole may be present.
Arranged in sheets, fascicles whorled, storiform or palisaded patterns.
GISTs (corpus) and some small and large intestinal GISTs are
spindle cell type.
Epithelioid GISTs were previously were known as epithelioid leiomyoblastoma.
Usually noted in gastric antrum.
Cell have abundant cytoplasm, round nuclei, cytoplasmic vacuoles and are arranged in sheets or nests.
Clear cell, signet ring, oncocytic and plasmacytoid variants may be noted.
(Gastrointestinal autonomic nerve tumours):
- Epithelioid cell component more prominent.
- Arborizing blood vessels and hemorrhagic spaces.
- Skeinoid fibres- (small eosinophilic, globular aggregates of filamentous material)
- Lymphocytic infiltrate in the stroma.
- Greater malignant potential and risk of metastasis.
6) GIST divided into four major groups:
- Differentiation towards smooth muscle cells.
- Differentiation towards neural elements.
- Dual differentiation (neural and smooth muscle).
- Lacking differentiation of either cell type.
7) Guidelines for predicting behaviour of tumour using size of tumour and mitotic count / 50 HPF (Berman 2001 ; Fletcher et al 2002).
50 high power field (HPF) is equivalent to 5 mm/square field.
In 40x lenses, 20 to 25 HPF to survey the same area.
Sites include esophagus, stomach,
small intestine, large intestine.
Size cm Mitotic count
Very low risk <2 <5
Low risk 2-5 <5
Intermediate risk < 5 6-10
> 5 > 5
> 10 any
Nearly always positive:
- c-kit gene product (CD117) - confirms the diagnosis.
- Smooth muscle actin and desmin
- S100 protein (specially in small bowel tumour)
- PGP9.5, neuron specific enolase, synaptophysin.
9) About 10-15 % of adult gastrointestinal stromal tumors (GISTs) and 85 % of pediatric GISTs do not have mutations in the KIT or PDGFRA genes and are generally classified as KIT/PDGFRA wild type (WT).
Recent studies have shown that this group of KIT/PDGFRA WT GISTs is quite heterogeneous in terms of clinical phenotype, genetic etiology, and molecular pathways.
Succinate dehydrogenase subunit (SDH)-deficient GISTs, which include tumors that are part of multiple endocrine neoplasia syndromes, are the newest group of KIT/PDGFRA WT GIST to be molecularly elucidated.
10) In a case of stromal tumour the report should include the following points;
- Tumour cell type: Spindle/ epithelioid
- Nuclear pleomorphism and its severity
- Number of mitotic figures / 50hpf
- Tumour to be categorized according to relative risk of malignant behaviour.
- Presence of absence of necrosis
- Extent of tumour involvement (depth of involvement, distance from resection margins and serosal margins and lymphnode metastases).
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