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Pathology of Gastrointestinal

Stromal Tumour (GIST)

Dr Sampurna Roy MD

 

                                                                                                                      

 

 

1) Gastrointestinal 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)

Esophagus- 5%

Stomach-  50-70%

Small intestine- 25-40%

Colorectal-   Less than 10%

Omentum, peritoneum, retroperitoneum- about 7%

 

3) Macroscopic features:

Single or multiple tumours.

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:

2 main cell types: Spindle and Epithelioid.

Spindle cells:  

Short. uniform, blunt ended, eosinophilic cytoplasm. Paranuclear vacuole may be present.

Arranged in sheets, fascicles whorled, storiform or palisaded patterns.

Most gastric GISTs (corpus) and some  small and large intestinal GISTs are spindle cell type.

Epithelioid cells: 

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.

 

5) GANT (Gastrointestinal autonomic nerve tumours):
 
- Diagnosed by presence of neuronal differentiation on  electron microscopy (dense core granules).

- 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.

Differential diagnosis:

Smooth muscle tumour ; Schwannoma; Inflammatory myofibroblastic tumour; Inflammatory fibrous polyp ;  Fibromatosis ; Solitary fibrous tumour; Glomus tumour

 

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

                            5-10        < 5

 

High risk              >  5         > 5
                     

                           > 10         any site
                         
any site       > 10

 

8)  Immunohistochemistry:

Nearly always positive:

- CD34

- c-kit gene product (CD117) -  confirms the diagnosis.

- Vimentin

Sometimes positive:

- Cytokeratin

- 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.

The genetic landscape of gastrointestinal stromal tumor lacking KIT and PDGFRA mutations.

 

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).

Gastrointestinal stromal tumors, intramural leiomyomas, and leiomyosarcomas in the rectum and anus: a clinicopathologic, immunohistochemical, and molecular genetic study of 144 cases. 

Gastrointestinal stromal tumors in the appendix: a clinicopathologic and immunohistochemical study of four cases.

 

 

Further reading:  

Google images

Gastrointestinal stromal tumors (GISTs): definition, occurrence, pathology, differential diagnosis and molecular genetics.

Pathology and diagnostic criteria of gastrointestinal stromal tumors (GISTs): a review.

Diagnosis of gastrointestinal stromal tumors: A consensus approach.

Gastrointestinal stromal tumors.  

Gastrointestinal stromal tumors, intramural leiomyomas, and leiomyosarcomas in the duodenum: a clinicopathologic, immunohistochemical, and molecular genetic study of 167 cases. 

Evaluation of malignancy and prognosis of gastrointestinal stromal tumors: a review.

Gastrointestinal stromal tumor: consistent CD117 immunostaining for diagnosis, and prognostic classification based on tumor size and MIB-1 grade.

Interstitial cells of Cajal as precursors of gastrointestinal stromal tumors.

 

 

Dr Sampurna Roy  MD

Consultant  Histopathologist (Kolkata - India)


 

 

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