Objective: To evaluate the prevalence of Fms-Like tyrosine kinase 3 (FLT3) mutations including internal tandem duplication (ITD) of juxtamembrane region and point mutation in the second tyrosine kinase domain (TKD) in acute promyelocytic leukemia (APL) and its clinical significance.
Methods: Bone marrow mononuclear cells from 160 newly diagnosed APL patients were analyzed. Polymerase chain reaction (PCR) was used to detect FLT3-ITD mutations, FLT3-ITD positive samples were further analyzed for the ITD allelic ratio (ITD-AR, mutant-wild type ratio). The FLT3-TKD mutation was analyzed by PCR amplification of exon 20 followed by EcoR V digestion and sequencing.
Results: Out of 160 patients, 30 (18.75%) patients were FLT3-ITD positive, 17 (10.62%) were FLT3-TKD positive, 2 had both of mutations. The initial WBC count and the ratio of short type PML-RAR alpha isoforms in FLT3-ITD positive and FLT3-TKD positive patients were all higher than that in patients with wild-type FLT3 (FLT3-wt) (P < 0.05). For FLT3-ITD positive patients, the incidences of retinoic acid syndrome (RAS) and disseminated intravascular coagulation (DIC) were 41.7% and 65.4%, respectively, being higher than that of FLT3-wt patients, while their complete remission (CR) rate was lower (69.2% vs 90.3%, P < 0.05). For FLT3-TKD positive patients, the incidence of RAS, DIC and CR rate were not significantly different from that of FLT3-wt patients (P > 0.05). FLT3-ITD positive patients had a shorter overall survival (OS) (P < 0.05), but not disease-free survival (DFS) (P > 0.05) as compared with FLT3-wt patients. There was no significant difference in either OS or DFS between FLT3-TKD positive and FLT3-wt patients. The ITD-AR of 30 FLT3-ITD positive patients varied from 0.11 to 6.55 with a median of 1.0. The initial WBC count, incidence of RAS and DIC, CR rate were not significantly different between the patients with ITD-AR greater than 1.0 and lower than 1.0 (P > 0.05).
Conclusions: FLT3 mutations (FLT3-ITD or FLT3-TKD) are frequently identified in patients with newly diagnosed APL, both mutations are associated with higher initial WBC and short type PML-RAR alpha isoforms. FLT3-ITD mutation is more frequent than FLT3-TKD mutation, and predicts a poorer prognosis, whereas FLT3-TKD mutation does not show the same unfavorable prognostic effect on APL patients.