Activating mutation of D835 within the activation loop of FLT3 in human hematologic malignancies

Mutations of receptor tyrosine kinases are implicated in the constitutive a ctivation and development of human malignancy. An internal tandem duplicati on (ITD) of the juxtamembrane (JM) domain-coding sequence of the FLT3 gene (FLT3/ITD) is found in 20% of patients with acute myeloid leukemia (AML) an d is strongly associated with leukocytosis and a poor prognosis. On the oth er hand, mutations of the c-KIT gene, which have been found in mast cell le ukemia and AML, are clustered in 2 distinct regions, the JM domain and D816 within the activation loop. This study was designed to analyze the mutatio n of D835 of FLT3, which corresponds to D816 of c-KIT, in a large series of human hematologic malignancies. Several kinds of missense mutations were f ound in 30 of the 429 (7.0%) AML cases, 1 of the 29 (3.4%) myelodysplastic syndrome (MDS) cases, and 1 of the 36 (2.8%) acute lymphocytic leukemia pat ients. The D835Y mutation was most frequently found (22 of the 32 D835 muta tions), followed by the D835V (5), and D835H (1), D835E (1), and D835N (1) mutations. Of note is that D835 mutations occurred independently of FLT3/IT D. An analysis in the 201 patients newly diagnosed with AML (excluding M3) revealed that, in contrast to the FLT3/ITD mutation (n = 46), D835 mutation s (n = 8) were not significantly related to the leukocytosis, but tended to worsen disease-free survival. All D835-mutant FLT3 were constitutively tyr osine-phosphorylated and transformed 32D cells, suggesting these mutations were constitutively active. These results demonstrate that the FLT3 gene is the target most frequently mutated to become constitutively active in AML. (Blood. 2001;97:2434-2439) (C) 2001 by The American Society of Hematology.