Test Details: The majority of gastrointestinal stromal tumours (GISTs) harbour oncogenic mutations in the gene encoding for the tyrosine kinase (TK) KIT. The most common mutations are found in exon 11, followed by mutations in exon 9. Exon 11, which encodes the juxtamembrane domain of KIT, is the most frequently mutated region, affecting 70–75% of GIST. Mutations in exon 9, which encodes the extracellular domain of KIT, occur in 7–15% of GIST cases.