Gastrointestinal Stromal Tumor (GIST)

 

  • – 1-3% of all malignant GI tumors
  • – 60-70% arise in stomach
  • – 20-30% in small intestine
  • – <10% in esophagus, colon, rectum
  • – Occurs predominantly in adults
  • Extra-intestinal sites:
  • – Omentum
  • – Mesentery
  • – Retroperitoneum
  • – Pancreas
  • Sites of metastasis:
  • – Liver
  • – Omentum
  • – Peritoneal cavity
  • – Lymph node metastasis is rare
  •              
  •            Clinical features:
  • – Depends upon the site of involvement
  • – Tumor size >5 cm causes symptomatic presentation
  •                        • Palpable abdominal mass
  •                        • Abdominal swelling
  •                        • Abdominal pain
  •                        • Nausea, vomiting, anorexia, early satiety
  •                        • Acute GI hemorrhage (40%)
  •                        • GISTs express a thyroid hormone inactivating enzyme that causes ‘consumptive’ type hypothyroidism requiring supranormal thyroid dose
  •                                            
  •                                                Diagnosis:
  • Biopsy:
  • – GISTs are highly vascular, soft and fragile tumor     May present an unacceptable risk for endoscopic biopsy
  • – Percutaneous biopsy/FNAC impose a risk of tumor rupture and tumor seeding along the biopsy tract or spread via peritoneal/mesenteric contamination
  • – Preoperative biopsy is not performed if resection is planned
  • – Preoperative biopsy must be performed in case of unresectable GIST to make diagnosis and to justify preoperative imatinib therapy
  • – FNA biopsy of gastric GIST using EUS guidance can be performed safely
  •                   
  •                   Pathology:
    • – Spindle cell type -70%
    • – Epithelioid type- 20%
    •            
    •   Immunohistochemistry:
    • – >95% are CD117 positive
    • – 5% are KIT-negative
    •                     • 80% in genotype analysis show mutation in the PDGFRA (Platelet derived growth factor receptor-alpha)
    •                     • KIT- negative (wild type) are less responsive to Imatinib and have a poor prognosis
    •        
    •              Prognostic factors for GIST:
    • – Tumor size (>2cm)
    • – Number of mitoses, reflecting proliferative activity of cells (5/50 HPF)
    • – Small intestinal GISTs have a less favorable prognosis than other GISTs
  •                                
  •                          
  •                                    Treatment:
    • Primary localized disease(Early-stage disease):
    •                   – Surgery followed by adjuvant imatinib therapy
    •                   – Imatinib delay tumor recurrence
    •                   – No role of radiotherapy
    • Advanced- stage disease
    •                   – Locally advanced, inoperable and metastatic disease
    •                                • Imatinib (400mg) for indefinite period of time
    •                                 Treatment interruption is generally followed by relatively rapid tumor progression
    • Side effects of Imatinib:
    •              • Edema
    •              • Nausea
    •              • Muscle cramp
    •              • Tachyphylaxis to Imatinib occur over a period of time

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