Gastrointestinal Stromal Tumor (GIST)
Definition
- Gastrointestinal tract associated mesenchymal neoplasm with activating mutation in KIT (CD117) or platelet derived growth factor A (PDGFRA)
Alternate/Historical Names
- Most gastric leiomyomas and leiomyosarcomas and virtually all leiomyoblastomas in the older literature would now be considered GIST
- Gastrointestinal stroma tumor (GANT) is now considered to be GIST
Diagnostic Criteria
- Encompasses most mesenchymal lesions of the GI tract
- Smooth muscle, fibroblastic and nerve sheath tumors are excluded (see Differential Diagnosis)
- Principal patterns are spindled or epithelioid, may be mixed
- Spindled 2/3 of cases
- Uniform spindle cells
- Pale eosinophilic, indistinct cytoplasm
- Oval to short spindled nuclei
- Frequently palisades
- May have paranuclear vacuoles
- May have skeinoid fibers
- Brightly eosinophilic bundles/globules of collagen
- Distinct from surrounding stroma
- Frequent retraction
- PAS/d positive
- Most common in small intestine
- Epithelioid 1/3 of cases
- Round/polygonal cells
- Round to oval nuclei
- Frequent cytoplasmic retraction creates clearing artifact
- May be discohesive
- Occasional to rare patterns and variants (may be superimposed on spindled or epithelioid patterns)
- Blood vessel walls may be hyalinized
- Calcification is frequent
- Chondroid
- Glandular (mucin and keratin negative)
- Myxoid
- Osteoclast-like giant cells
- Paraganglioma-like pattern (chromogranin and synaptophysin negative)
- Rhabdoid or rhabdomyomatous
- Sclerosing
- Usually small and benign
- May calcify
- Signet ring (mucin and keratin negative)
- Rhabdomyosarcoma has been reported following Imatinib therapy
- CD117/KIT positive
- 95% sensitive
- Specific in the right pathological and clinical context
- May occur throughout the GI tract
- Nearly all GI cases involve muscularis propria
- Most common in stomach
- Rare in esophagus and large intestine
- Rare extra-GI cases reported
- Identical histology, immunohistology and genetic defects as usual GIST
- If metastasis is ruled out, these may be designated as extra-GI GIST
- Responses to Imatinib mesylate have been reported in such cases
- Most in omentum and mesentery
- Solitary omental GIST are generally considered to be detached gastric primaries
- Rarely in gall bladder, pancreas, liver, urinary bladder, vagina
- Gastrointestinal autonomic nerve tumor (GANT)
- Presently considered to fall within the spectrum of GIST
- We do not make this diagnosis
- Malignant cases typically exhibit peritoneal spread
- Metastases may be seen to liver, lungs, bone
- Lymph node metastases very rare except in pediatric (and adult pediatric-type) cases
- Size and mitotic rate are predictive of behavior (see Grading)
- Incidental microscopic (seedling) GIST
- They can be found in up to 10% of esophagogastrectomies
- Rarer in other sites
- Rare cases may be multiple or hereditary or pediatric
- May be associated with other neoplasms
- Pediatric type metastasizes to lymph nodes
- One series of pediatric type occuring in adults (Rege 2011)
- Does not include multiple incidental microscopic GIST
Teri A Longacre MD
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342
Original posting/last update : 12/2/09, 8/13/11, 12/4/11
