Detection of a new mutation in KIT exon 9 in a gastrointestinal stromal tumor.

Gastrointestinal stromal tumors are mesenchymal tumors arising in the stomach and small bowel and more rarely in the rectum, esophagus, peritoneum and retroperitoneum. These tumors are characterized by KIT or PDGFRA mutations. KIT mutations are all in frame and lead to constitutive tyrosine kinase domain activation without ligand binding. Mutations concern four exons (9, 11, 13 and 17) but mainly exon 11. We report a new mutation in exon 9, since only AY 502-503 duplication/insertion, FAF 506 insertion and P456S substitution have been previously reported. This mutation consists of a large deletion of 43 nucleotides and an insertion of 25 nucleotides. More surprisingly, the sequence inserted corresponds to the complementary sequence of the wild allele but in the opposite sense. To our knowledge, this mutation has never been previously described.