FLT3 Internal Tandem Duplications in Adults with De Novo Acute Myeloid Leukemia.

FLT3 is a receptor tyrosine kinase involved in the proliferation and differentiation of hematopoietic stem cells. Recently, internal tandem duplication (ITD) mutations of the FLT3 gene have been described in patients with AML and associated with a poor prognosis. The aim of this study was to analyze the prevalence of FLT3-ITD in a series of 90 adults with de novo AML and correlate the presence of this mutation with biological characteristics and clinical response. We analyzed diagnostic peripheral blood or bone marrow specimens from 43 women and 47 men, with a median age of 38 years (16–83). Polymerase chain reaction was performed on genomic DNA using previously published primers for exons 11 and 12. An FLT3-ITD was found in 22/89 patients (25%). It was present in 37% (9/24) of the patients with acute promyelocytic leukemia (APL) and in only 20% (13/65) of the patients with non-M3-AML (p=0.07). The FLT3-ITD was not detected in patients with M6 (n=1) and M7-AML (n=3), nor in patients with the AML1-ETO (n=2) or with the CBFb-MYH11 (n=4) fusion genes. The median WBC counts were higher in FLT3-ITD patients than in those without the mutation (37 X 10⁹/L vs. 27 X 10⁹/L, p=0.43). In APL, FLT3-ITD was found in 5 out of 6 patients with the short PML-RARa isoform, but in only 4 out of 18 patients with the non-short isoform (p=0.01). Univariate analysis showed an association between the presence of FLT3-ITD and both a lower complete remission (CR) rate (41% vs. 64%; p=0.05) and a shorter overall survival (14% vs. 34%; p=0.03). However, FLT3-ITD was not associated with the CR rate (p=0.18) or the OS (p=0.07) in the multivariate analysis. The clinical significance of FLT3-ITD in adult AML remains uncertain, and further investigation is clearly warranted.