However, in addition to its activity for bcr-abl, imatinib also blocks the activity of several rtks, including the Kit and pdgf receptors, and has shown robust clinical activity in a subset of gastrointestinal stromal tumours and in chronic myelomonocytic leukemia harbouring mutations in the Kit or pdgf receptors 14. This evidence concerns the gene KIT and chronic myelomonocytic leukemia.