KIT and mesenchymal cell neoplasm: Gastrointestinal stromal tumours (GIST) are the most common mesenchymal tumours of the gastrointestinal tract, and the majority of adult onset GIST, so-called ‘tyrosine kinase mutant’ GIST (TK-mutant GIST), are driven by activating somatic mutations in the KIT [1] or PDGFRA [2] genes.