Internal tandem duplication and Asp835 mutations of the FMS‐like tyrosine kinase 3 (FLT3) gene in acute promyelocytic leukemia

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Abstract
BACKGROUND The clinical relevance of mutations of the FMS‐like tyrosine kinase 3 (FLT3) gene in specific cytogenetic subgroups is not clear. The authors examined internal tandem duplication (ITD) and Asp835 mutations of FLT3 in patients with acute promyelocytic leukemia (APL) to determine the incidence of these mutations and to analyze the results for correlations with clinicohematologic features and outcome. METHODS Bone marrow samples from 107 patients with APL were analyzed. Isoforms of PML‐RARα were identified using a reverse transcription–polymerase chain reaction assay. A standard polymerase chain reaction (PCR) assay was used to detect FLT3/ITD mutations. Asp835 mutations were analyzed by PCR amplification of exon 20 followed by EcoRV digestion. All aberrant PCR products subsequently were sequenced. RESULTS Twenty‐two patients had FLT3/ITD mutations: 9 of 63 patients with L‐type PML/RARα, 13 of 34 patients with S‐type PML/RARα, and 0 of 10 patients with V‐type PML/RARα (P = 0.005). The incidence of FLT3/ITD mutations was significantly higher in patients with S‐type PML/RARα than in patients with L‐type PML/RARα or V‐type PML/RARα. Twenty patients had Asp835 mutations (L‐type PML/RARα: n = 11; S‐type PML/RARα: n = 8; V‐type PML/RARα: n = 1). The frequency of Asp835 mutations was not significantly different among patients with different PML/RARα isoforms (P = 0.582). Three patients had both ITD and Asp835 mutations. The microgranular variant (M3v) form of leukemia was found to be associated with a higher frequency of ITD (P = 0.002) but not with a higher frequency of Asp835 mutations (P = 1.000); analysis of clinicohematologic variables revealed no significant differences in FLT3 mutation incidence among other patient subgroups. There was no significant difference in complete remission rate, overall survival, or event‐free survival between patients with ITDs and those without ITDs or between patients with Asp835 mutations and those without Asp835 mutations. CONCLUSIONS The current study found that ITD or Asp835 mutations of the FLT3 gene were present in 36.4% of patients with APL; however, these mutations had no prognostic impact. FLT3/ITD frequently was associated with S‐type PML/RARα and with the M3v form of leukemia. Cancer 2003;98:1206–16. © 2003 American Cancer Society. DOI 10.1002/cncr.11636

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