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

Abstract

BACKGROUNDThe 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.METHODSBone 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.RESULTSTwenty‐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.CONCLUSIONSThe 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

A distinctive nuclear morphology in acute myeloid leukemia is strongly associated with loss of HLA-DR expression and FLT3 internal tandem duplication

“…However, it should be noted that microgranular APL has frequent nuclear invagination imparting a bilobed appearance to the nucleus (but not cup-like nuclear indentation), is HLA-DR-negative, and also has a high rate of the Flt3 ITD. [24][25][26] Therefore, among the well-characterized types of AML, microgranular APL appears to be most similar to AML-cuplike. Although the AML-cuplike and microgranular APL data suggest a general relationship between the Flt3 ITD and prominent nuclear invagination in AML, additional studies will be necessary to determine whether there is a mechanistic relationship between constitutive activation of the Flt3 tyrosine kinase and nuclear invagination, and whether the rare AML-cuplike cases without Flt3 mutations (three of 19 in our series) harbor activating mutations in other components of the Flt3 signaling pathway.…”

Gene expression profiling of acute promyelocytic leukaemia identifies two subtypes mainly associated with Flt3 mutational status

“…Interestingly, Flt3-ITDs appear to be frequently associated to leukocytosis, M3v form and to the presence of the short PML/RARa isoform (bcr3). 13,16,22,46 We decided to examine the gene expression profiles by microarray containing approximately 20 000 human genes of 18 t(15;17) APL cases looking for correlation with clinical, morphological, and molecular features. As expected, APL demonstrated a homogeneous pattern of gene expression (Figure 1a) characterized by a very high correlation coefficient (Pearson correlation coefficient range ¼ 0.90-0.98) among all the samples examined.…”

“…Moreover, the presence of ITDs in Flt3 gene was related to microgranular morphology (M3v) (Po0.0001) and short-type PML/RARa isoform (bcr3) (P ¼ 0.042), as previously described. 16,22,23 Flt3 activation loop mutations were present in five of 29 (17.2%) APL patients (Flt3-ALM group). We found the presence of a missense mutation at codon 835 in four cases and a six-base pair deletion together with a missense mutation at codon 836 in one case.…”

Acute promyelocytic leukemia: where does it stem from?

“…There is an intriguing correlation between PML-RARa isoform, FLT3 ITD and morphological features, [76][77][78] (Figure 3) and it will be interesting to dissect out to what extent the morphological features and leukocytosis associated with M3v reflect the targeting of a more primitive progenitor and/or the expression of the short isoform of PML-RARa or presence of activating mutations of FLT3. This raises even more fundamental questions regarding the mechanisms by which APL-associated translocations arise in the first place and whether distinct subsets of progenitors have differing propensities to the development of particular chromosomal breakpoints.…”