Diagnosis
Histopathology
Definitive diagnosis of GIST requires tissue biopsy of resected material and evaluation by an experienced pathologist. Small tissue samples are often inconclusive, as the histologic appearance of the tumour can vary throughout a single mass and can change with therapy.1 Fixed tissue samples are evaluated in the surgical pathology laboratory, by light microscopic examination after thin sectioning and staining with a general morphological stain such as haematoxylin and eosin.
Histologically, GISTs can be classified into 3 broad categories: spindle-cell type (70%), epithelioid type (20%), and mixed spindle and epithelioid cell type (mixed morphology) (10%).2 GISTs have a remarkably uniform appearance, with only a small minority having a notable cytologic pleomorphism (<2% to 3%).3
Figure 1
Spindle Cell Epithelioid Cell Mixed Morphology
Figure 1. GIST histopathological cell types. Images reproduced from Fletcher CD, et al. Hum Pathol. 2002;33:459-465.
GISTs with spindle-cell type morphology have relatively uniform eosinophilic cells arranged in short fascicles or whorls. In relation to smooth muscle neoplasms, GISTs have a paler eosinophilic cytoplasm with more ovoid/shorter nuclei.3 GISTs of epithelioid type morphology have rounded cells with variably eosinophilic or clear cytoplasm.3
References:
1. Pauwels P, Debiec-Rychter M, Stul M, De Wever I, Van Oosterom AT, Sciot R. Changing phenotype of gastrointestinal stromal tumours under imatinib mesylate treatment: a potential diagnostic pitfall. Histopathology. 2005;47:41-47.
2. 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.
3. Fletcher CDM, Berman JJ, Gorstein F, et al. Diagnosis of gastrointestinal stromal tumors: a consensus approach. Hum Pathol. 2002;33:459-465.