GIST patients may also present with:
- An acute abdomen caused by tumor rupture.
- GI obstruction.
- Appendicitis-like pain.
Other clinical symptoms include the following:
Smaller lesions may be incidental findings during surgery, radiologic studies, or endoscopy. The natural history of these incidental tumors and the frequency of progression to symptomatic disease are unknown. There may be a substantial reservoir of small GIST tumors that do not progress to symptomatic stages. For example, a series of 98 consecutive systematic autopsies on adults who died of unrelated causes revealed grossly recognizable gastric tumors (1 mm–6 mm) that were histologically diagnosed as GIST in 22.5% of cases. Sufficient DNA was available for analysis in 26 patients, revealing 13 patients with mutations in KIT exon 11 and one in PDGFRA.
In a retrospective study of 200 GIST cases, typical clinical manifestations of malignancy included liver metastases and/or dissemination within the abdominal cavity. Lymph node involvement and spread to the lungs or other extra-abdominal sites was unusual. Advanced disease may be associated with metastases to distant sites, including lung and bone. Brain metastases are rare.
GIST should be included in the differential diagnosis of any intra-abdominal nonepithelial malignancy. Diagnostic interventions may include the following:
- Computed tomography (CT).
- Magnetic resonance imaging.
- Upper GI endoscopy.
Tests that may be useful in staging include the following:
- 18 FDG-PET (18 fluoro-deoxyglucose-positron emission tomography).
Endoscopic ultrasound with fine-needle aspiration biopsy is useful in the detection of GIST in the upper GI tract because most tumors arise below the mucosal layer and grow in an endophytic fashion.[12,13,14]
Because nodal metastasis is so rare at diagnosis (i.e., it is virtually unheard of for true GIST according to the AJCC Cancer Staging Manual), there is general agreement that nodal dissection is not needed.
Pathology and Molecular Genetics
Typically arising within the muscle wall of the GI tract, GIST range in size from less than 1 cm to more than 40 cm, with an average size of approximately 5 cm when diagnosed clinically. Small GIST may form solid subserosal, intramural, or, less frequently, polypoid intraluminal masses. Large tumors tend to form external masses attached to the outer aspect of the gut involving the muscular layers. GIST morphology is quite varied; the tumors are composed of the following:
- Spindle cells (70%).
- Epithelioid cells (20%).
- Mixed spindle and epithelioid cells (10%).