FLT3 Gene Mutations as a Prognostic Factor for Acute Myeloid Leukemia

Soon Hee Chang; Nan Young Lee; Dong Hwan Kim; Sang Kyun Sohn; Jang Soo Suh

doi:10.3343/kjlm.2006.26.4.233

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Chang, Lee, Kim, Sohn, and Suh: FLT3 Gene Mutations as a Prognostic Factor for Acute Myeloid Leukemia

Original Article

Korean J Leg Med 2006;26(4):233-240.

Published online: 10 February 2006

DOI: https://doi.org/10.3343/kjlm.2006.26.4.233

FLT3 Gene Mutations as a Prognostic Factor for Acute Myeloid Leukemia

Soon Hee Chang, M.D.¹, Nan Young Lee, M.D.², Dong Hwan Kim, M.D.³, Sang Kyun Sohn, M.D.³, Jang Soo Suh, M.D.⁴

¹Department of Laboratory Medicine, Daegu Fatima Hospital, Daegu, Korea

²Sungyoon Reference Laboratory, Daegu, Korea

³Department of Hematology/Oncology, School of Medicine, Kyungpook National University, Daegu, Korea

⁴Department of Clinical Pathology, School of Medicine, Kyungpook National University, Daegu, Korea

Received 15 November 2005 Revised 20 April 2006 Accepted 28 May 2006

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background

Two distinct types of fms-like tyrosine kinase 3 (FLT3) gene mutations have been identified in acute myeloid leukemia (AML): D835 and internal tandem duplication (ITD) mutations. These mutations are known to cause the proliferation of leukemic cells and inhibit the apoptosis of leukemic cells due to ligand-independent activation of their receptors. Therefore, the current study attempted to investigate the frequency of FLT3 gene mutations and their prognostic implications for AML in terms of treatment response, survival, and relapse.

Methods

Polymerase chain reaction (PCR) was performed to detect D835 and ITD mutations in 84 newly diagnosed AML patients from February 2001 to October 2004. Restriction fragment length polymorphism (RFLP) and direct sequencing were performed to analyze the D835 mutations. The results were examined based on a comparison with previously known prognostic factors, and the treatment outcomes analyzed according to the existence of the mutations in relation to the event free survival (EFS), overall survival (OS), and complete remission (CR) rates.

Results

D835 and IDT mutations were detected in 4.7% (4/84) and 19.0% (16/84), respectively, of the AML patients. The FLT3 gene mutations were not found to be associated with previously known prognostic factors, such as the WBC count, age, and cytogenetic risk group, but were associated with the lactate dehydrogenase levels. The EFS and OS rates were also significantly lower in the FLT3 gene mutation group, especially in AML with normal karyotypes.

Conclusions

FLT3 gene mutations were observed in 23.8% of AML patients and appeared to have a prognostic implication on patient survival. Accordingly, the presence of FLT3 gene mutations, which could be tested easily by using PCR/RFLP methods, should be investigated routinely at the time of diagnosis.

Keywords: FLT3, Acute myeloid leukemia, Prognostic implications

References

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Fig. 1.

Results of D835 mutations in the FLT3 gene. The amplified product (lane 1) of wild type was digested to two bands (68 bp and 46 bp) by EcoRV in lane 2. When amplified products contained D835 mutations, undigested bands (114 bp) were visualized on low melting point agarose gel electrophoresis (lane 3 and 4). Lane SM, molecular size markers (100 bp DNA ladder).

Fig. 2.

Sequence analysis in 3 patients with D835 mutations in the FLT3 gene. The results revealed that the first nucleotide G of codon 835 was substituted with T.

Abbreviation: FLT3, fms-like tyrosine kinase 3.

Fig. 3.

Results of ITD mutations in the FLT3 gene. The amplified product of wild type was shown in lane 5. When amplified products contained ITD mutations, another bands were visualized on low melting point agarose gel electrophoresis (lane 1–4). Lane SM, molecular size marker (100 bp DNA ladder).

Fig. 4.

Event free (A) and overall (B) survival in patients with AML according to the FLT3 mutation status.

Fig. 5.

Event free (A) and overall (B) survival rate in patients with normal karyotype in AML according to the FLT3 mutation status. Abbreviations: AML, acute myeloid leukemia; FLT3, fms-like tyrosine kinase 3; ITD, internal tandem duplication; FLT3⁺, FLT3 mutation; FLT3^-, no FLT3 mutation.

Table 1.

Results of analysis for D835 and ITD mutations in the FLT3 gene

Subtype of AML	N of patient	FLT3 mutations (%)	D835 mutations (%)	ITD mutations (%)
M0	5	0 (0)	0 (0)	0 (0)
M1	2	1 (50.0)	1 (50.0)	0 (0)
M2	42	8 (19.0)	1 (2.4)	7 (16.7)
M3	7	3 (42.9)	1 (14.3)	2 (28.6)
M4	11	4 (36.4)	0 (0)	4 (36.4)
M5	9	3 (33.3)	1 (11.1)	2 (22.2)
M6	5	1 (20.0)	0 (0)	1 (20.0)
M7	3	0 (0)	0 (0)	0 (0)
Total	84	20 (23.8)	4 (4.8)	16 (19.0)

Abbreviations: FLT3, fms-like tyrosine kinase 3; AML, acute myeloid leukemia; ITD, internal tandem duplication.

Abbreviation: FLT3, fms-like tyrosine kinase 3.

Abbreviations: FLT3, fms-like tyrosine kinase 3; ITD, internal tandem duplication.

Table 2.

Relationship between known prognostic factors and the FLT3 mutations

Prognostic factors	N of patient	FLT3 mutations		P value
Prognostic factors	N of patient	Positive	Negative	P value
WBC (/μL)
≥50,000	22	5	17	NS
<50,000	62	11	51
LD (U/L)
≥1,000	33	12	21	0.013
<1,000	43	5	38
Age (years)
≥50	35	6	29	NS
<50	49	14	35
Cytogenetic findings^*
Favorable group	17	6	11	NS
Intermediate group	45	11	34
Unfavorable group	15	3	12

^* Favorable group: t(15;17), t(8;21), and inv(16); intermediate group: normal karyotype and other karyotypes; unfavorable group: −7, −5, del(11q23), and complex karyotype.

Abbreviation: NS, not significant.

Table 3.

Comparison of survivals and complete remission rates excluding M3 according to the FLT3 mutation status

	FLT3 mutations		P value
	Positive (N=9)	Negative (N=42)	P value
EFS
Median (days)	135	429	0.018
1 YEFS rate (%)	0	57.0±8.5^*
OS
Median (days)	336	793	0.007
1 YOS rate (%)	45.7±16.6	67.8±8.0
CR
Rate (%)	77.8	71.4	NS

^* Mean±SD.

Abbreviations: FLT3, fms-like tyrosine kinase 3; EFS, event free survival; YEFS, year event free survival; OS, overall survival; YOS, year overall survival; CR, complete remission; NS, not significant.

Table 4.

Comparison of survivals excluding M3 according to the FLT3 mutation status among the patients with a normal karyotype

	FLT3 mutations		P value
	Positive (N=11)	Negative (N=28)	P value
EFS Median (days)	135	NR	0.001
OS Median (days)	336	NR	0.005

Abbreviations: See Table 3. FLT3, fms-like tyrosine kinase 3; NR, not reached.

Abbreviations: AML, acute myeloid leukemia; FLT3, fms-like tyrosine kinase 3; ITD, internal tandem duplication; FLT3⁺, FLT3 mutation; FLT3^-, no FLT3 mutation.

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