GIST Management
Diagnosis
Imaging and Biopsy
The differential diagnosis of gastrointestinal stromal tumours (GIST) is complex. GIST may be differentiated from other GI tumours such as leiomyosarcomas, leiomyomas, schwannomas, malignant melanoma, and fibromatosis. Available imaging modalities to evaluate GIST include:
- CT
- Endoscopic ultrasound
- Magnetic resonance imaging (MRI)
- Fluorine-18-fluoro-deoxyglucose (FDG) positron emission tomography (PET)
Contrast-enhanced CT scan is the imaging modality of choice to visualise suspected abdominal masses,1 and is used in staging and surgical planning. CT scanning provides for visualisation of the full extension of large exophytic GIST masses (tumour grows between the bowel loops) and sometimes within the bowel lumen, and is able to detect local invasion as well as distant metastases. CT scanning also helps to guide tissue biopsy. A small tumour found incidentally during endoscopy can be evaluated using endoscopic ultrasound or CT.
MRI is the procedure of choice for imaging rectal GISTs because it provides better soft-tissue contrast resolution and direct multiplanar imaging, and a better delineation of tissues.
PET may help to distinguish tissue functionalities-such as the difference between recurrent tumour and scar tissue-or in highlighting early functional changes and responses to treatment. Evaluation of FDG uptake using PET scanning is recommended when an early detection of response to Glivec treatment is required, eg, to consider surgery after Glivec cytoreduction of rectal tumours.1 PET scan may also be useful in judging cases suspected to be metastatic.
GISTs are fragile and may bleed easily. If a suspected GIST is considered to be resectable after primary workup, then biopsy before surgery is not recommended because the risk of tumour spill and cellular dissemination is high. However, if a preoperative biopsy is scheduled, an experienced multidisciplinary team is preferred.1
The diagnosis of GIST relies on standard histologic examination and immunohistochemical analysis of several markers, including KIT. Equivocal cases should be submitted to a central review by an expert in sarcoma pathology, experienced in the diagnosis of GIST.1
References:
1. Blay JY, Bonvalot S, Casali P, et al. Consensus meeting for the management of gastrointestinal stromal tumors. Report of the GIST Consensus Conference of 20-21 March 2004, under the auspices of European Society for Medical Oncology. Ann Oncol. 2005;16:566-578.