Gastrointestinal stromal tumour
Gastrointestinal stromal tumours (GISTs) are mesenchymal gastrointestinal neoplasms that occur anywhere in the gastrointestinal tract, but are most common in the stomach (~66%) followed by the small intestine (~33%). Most are located within the wall, and arise in the deep muscle layers. These tumors used to be thought of as leiomyomas or leiomyosarcomas, as they looked like smooth muscle tumours found elsewhere in the body. GISTs are well-circumscribed and may push up and ulcerate the overlying mucosa (like carcinoid tumours). Histologically, most are composed of spindle shaped cells with variable numbers of mitotic figures.
Clinically, stromal tumours occur at all ages and may represent incidental findings if small or be associated with pain, bleeding or obstruction. Currently, the most reliable determinants of malignant behaviour appear to be large size (>5 cm), and high mitotic rate (>2 mitoses in 50 high power microscopic fields). Assessment of these pathological factors allows stromal tumors to be categorized as being of either low, intermediate or high risk of aggressive behavior (recurrence or metastasis).