Stomach: Gastrointestinal Stromal Tumor (GIST)

Gastrointestinal Stromal Tumor (GIST)

Basics

  • Origin: Interstitial Cells of Cajal
  • Third Most Common Primary Gastric Malignancy – After Adenocarcinoma & Lymphoma
  • Most Common Sites:
    • Stomach (> 50% – Most Common)
    • Small Intestine (25-35%)
    • Colon (10%)
    • Rectum (5%)
    • Esophagus (2%)
  • Usually ASx

Malignancy

  • Most Often Benign but Can be Malignant
  • Spread: Hematogenous
  • Most Common Site of Metastases: Liver

Predictors of Poor Prognosis Mn

  • Size > 5 cm
  • Mitoses > 5/50 High-Powered Fields
  • Non-Gastric Site

GIST Specimen 1

Small Bowel GIST 2

TNM Staging

  • TNM
  T N M
1 ≤ 2 cm LN Mets
2 > 2 cm
3 > 5 cm
4 > 10 cm
  • Stage
    • *HMR = High Mitotic Rate
  T Mitotic Rate N M
I A T1-2 Low N0 M0
B T3 Low N0 M0
II   T4 Low N0 M0
  T1-2 HMR N0 M0
III A T3 HMR N0 M0
B T4 HMR N0 M0
IV   Any T Any N1 M0
  Any T Any Any N M1

Diagnosis

  • CT May Be Sufficient for Diagnosis if Appearance Typical
    • Biopsy May Risk Hemorrhage within the Tumor & Tumor Rupture/Dissemination
  • Endoscopic Bx/FNA if Needed
    • Seen as Bulging Mass with Normal Mucosa or Small Mucosal Ulcerations
    • Immunochemistry:
      • C-KIT/CD117 (Most Common) Mn
      • CD34 Positive
    • Histology: Bland Spindle Cells with Elongated Nuclei

Treatment

  • ASx & < 2 cm: Can Observe
  • Sx or > 2 cm: Resection
    • Margin: Resect All Macroscopic Disease (Usually 1 cm)
      • No Difference Between R0 & R1 Resection
    • No Lymph Node Dissection Needed
    • Imatinib (Tyrosine Kinase Inhibitor) Indications:
      • Neoadjuvant if Not Easily Resectable
      • Adjuvant if Intermediate-High Risk of Recurrence – Generally Taken for 3 Years
  • Metastatic or Recurrence: Imatinib
    • If Responds: Resection or Ablation
    • If Fails: Other TKI (Sunitinib or Regorafenib)

GIST of the Stomach 3

GIST Resection 4

Mnemonics

GIST Poor Predictors

  • “Rule of 5’s”
    • GIST = GI‘5’T
  • Size > 5 cm
  • Mitoses > 5/50 High-Powered Fields

GIST Immunochemistry

  • C-KIT & CD117

References

  1. Beham AW, Schaefer IM, Schüler P, Cameron S, Ghadimi BM. Gastrointestinal stromal tumors. Int J Colorectal Dis. 2012 Jun;27(6):689-700. (License: CC BY-NC-2.0)
  2. Okasha HH, Amin HM, Al-Shazli M, Nabil A, Hussein H, Ezzat R. A duodenal gastrointestinal stromal tumor with a large central area of fluid and gas due to fistulization into the duodenal lumen, mimicking a large duodenal diverticulum. Endosc Ultrasound. 2015 Jul-Sep;4(3):253-6. (License: CC BY-NC-SA-3.0)
  3. Bogoevski D, Mann O, Schurr P, Izbicki JR, Strate T. Laparoscopic gastric tailoring for huge subcardial gastrointestinal stromal tumor. JSLS. 2007 Jul-Sep;11(3):394-7. (License: CC BY-NC-ND-3.0)