gastrointestinal%20stromal%20tumor
GASTROINTESTINAL STROMAL TUMOR
Gastrointestinal stromal tumors are morphologically spindle cell, epithelioid, or occasionally pleomorphic mesenchymal tumors of the gastrointestinal tract.
Signs and symptoms of gastrointestinal tumor include presence of abdominal mass (which may be an incidental finding in endoscopy), gastrointestinal bleeding, hemoperitoneum, anemia and gastrointestinal perforation.

Laboratory Tests

Biopsy

  • Morphologic diagnosis from histologic microscopic examination is the standard for diagnosis
    • Diagnosis of primary gastrointestinal stromal tumor (GIST) is confirmed w/ a biopsy before starting preoperative therapy
  • GISTs are soft and fragile & may cause hemorrhage & increased dissemination
    • Pseudocapsule should be preserved & tumor spillage avoided
  • Endoscopic ultrasound-fine-needle aspiration (EUS-FNA) biopsy is preferred over percutaneous biopsy & may be done in GISTs <2 cm
  • Metastatic disease may be confirmed via percutaneous image-guided biopsy

Histopathology summary should include the following:

  • Diagnosis
    • Tumor type (eg spindle, epithelioid or mixed), mitotic rate
    • Presence or absence of necrosis, hemorrhage & lymphovascular invasion
    • Invaded structures
  • Immunohistochemistry result, KIT expression status
  • Margin evaluation
  • Prognostic category; prognostic factors include:
    • Mitotic rate
    • Tumor size & site
      • Gastric GISTs <2 cm are usually benign but colonic GISTs <2 cm w/ mitotic activity can recur & metastasize
      • Small bowel or colonic GISTs have an aggressive behavior compared w/ gastric GISTs
    • Surgical margin
    • Tumor rupture (has a highly adverse prognosis)
  • Recommendation on a multidisciplinary team meeting

Imaging

  • Abdominal/pelvic computed tomography (CT) scan w/ contrast
    • Allows assessment of primary tumor & extent of metastasis; investigation of choice for staging & follow-up
    • For incidentally found mass on endoscopy, CT may be performed if endoscopic ultrasound is not available
    • Initial imaging done for large palpable masses or for patients presenting w/ hemorrhage, abdominal pain or obstruction
    • Gastrointestinal stromal tumor (GIST) usually shows an extraluminal mass arising from the digestive tract wall
  • Magnetic resonance imaging (MRI)
    • Gives better preoperative staging data regarding rectal GISTs
    • May provide tumor localization & relationship w/ adjacent organs
  • Positron emission tomography (PET)
    • Provides early neoplastic information
    • Detects metabolic changes within the tumor earlier than the visible changes
    • May be used as part of the pre-operative assessment
    • May also be used to assess responsiveness of the tumor to Imatinib
  • Chest x-ray
  • Endoscopic ultrasound (EUS)
    • Should be performed first if submucosal mass is an incidental endoscopic finding
    • Important in diagnosis of small masses (<2 cm)
    • Most useful in assessment of masses located in the esophagus, stomach, duodenum & anorectum
    • Potential high-risk features include cystic spaces, echogenic foci, heterogeneity, irregular border, & ulceration
  • Endoscopy (if not yet done)
  • Mutational analysis
    • Performed when diagnosis is uncertain for mutations involving KIT & platelet-derived growth factor receptor alpha (PDGFRA) genes
      • Testing for these genes is strongly recommended
    • Genotyping must be performed when medical treatment is planned
      • Helps in identifying genotypes that will benefit from Imatinib therapy & the appropriate dose for treatment of KIT exon 9 mutations
    • If KIT or PDGFRA mutations are lacking, consider testing for germline mutations in the succinate dehydrogenase (SDH) genes

Diagnostic Approaches

  • For a <2-cm esophagogastric or duodenal nodule, laparoscopic/laparotomic excision is considered for histological diagnosis as endoscopic biopsy may be difficult
  • Rectal or recto-vaginal space nodules are biopsied/excised regardless of tumor size as risk is high for a GIST at this location
  • Laparoscopic/laparotomic excision may be performed for abdominal nodules not amenable to endoscopic assessment
  • Multiple core needle biopsies via endoscopic ultrasound guidance for a mass that is likely to have a multi-organ resection
  • For obvious metastases, diagnostic biopsy of the metastases is sufficient & may not need laparotomy
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