Gastrointestinal stromal tumours

 Definition

 • Mesenchymal tumours of variable malignant potential which arise within the wall of the GI tract and recapitulate the phenotype of the interstitial cell of Cajal, the pacemaker cell of the Auerbach plexus.

 Epidemiology

 • Incidence of about ~15 per million population per year.

 • Most arise in adults at a median age of 50– 60 y.

 Aetiology

 • Aetiology of sporadic cases unknown.

• A small proportion arise in association with neurofibromatosis type 1 and Carney’s triad, and in families with germline KIT mutations.

Genetics

 • the vast majority show activating mutations of the oncogene KIT.

 • the remainder show activating mutations in the related gene PDGFRA.

 Presentation

 • Palpable upper abdominal mass, pain, or bleeding.

 • Malignant tumours may cause symptoms related to metastasis.

 Sites of involvement

• Can occur anywhere in the GI tract, from the oesophagus to the rectum.

 • Most arise in the stomach (60– 70%) or small intestine (20– 30%).

 • A small number appear to arise primarily within the omentum.

 Macroscopy

 • Well- defined tumour mass centred on the submucosal, muscular, or serosal layer of the bowel.

 • range in size from 1 to >20 cm.

 Histopathology

 • Composed of spindle cells, often with paranuclear vacuoles. Plumper epithelioid cells may also be present and some tumours may be entirely epithelioid in nature.

• Small intestinal tumours may also have so- called skeinoid fibres.

• Almost all express the markers CD117 (c- kit) and DOG- 1. tumours treated with imatinib often show diminished staining.

 • Molecular detection of CD117 or PDGFRA mutations may be necessary in a minority of cases and is indicted in cases which are CD117 negative.

 Prognosis

 • Based on location, size, and mitotic activity, they are stratified into very low risk, low risk, intermediate risk, and high- risk categories for progressive disease. Generally, those arising in the stomach carry a better prognosis than those arising in the rest of the gastrointestinal tract.