Gastrointestinal%20stromal%20tumor Diagnosis
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
- Performed when diagnosis is uncertain for mutations involving KIT & platelet-derived growth factor receptor alpha (PDGFRA) 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