Prognostic Significance of FLT3 Internal Tandem Duplication in Acute Myeloid Leukemia with Normal Karyotype

Ja Young Lee; Young Don Joo; Seung Hwan Oh; Jeong Hwan Shin; Hye Ran Kim; Sang Min Lee; Jeong Nyeo Lee

doi:10.5045/kjh.2009.44.2.74

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Lee, Joo, Oh, Shin, Kim, Lee, and Lee: Prognostic Significance of FLT3 Internal Tandem Duplication in Acute Myeloid Leukemia with Normal Karyotype

Original Article

Korean J Hematol 2009;44(2):74-81.

Published online: 20 June 2009

DOI: https://doi.org/10.5045/kjh.2009.44.2.74

Prognostic Significance of FLT3 Internal Tandem Duplication in Acute Myeloid Leukemia with Normal Karyotype

Ja Young Lee, M.D.¹, Young Don Joo, M.D.², Seung Hwan Oh, M.D.¹, Jeong Hwan Shin, M.D.^1,³, Hye Ran Kim, M.D.¹, Sang Min Lee, M.D.², Jeong Nyeo Lee, M.D.^1,^3,

¹Department of Laboratory Medicine, Inje University College of Medicine, Busan, Korea

²Department of Internal Medicine, Inje University College of Medicine, Busan, Korea

³Department of Paik Institute for Clinical Research Busan Paik Hospital, Inje University College of Medicine, Busan, Korea

Correspondence to：Jeong Nyeo Lee, M.D., Ph.D. Department of Laboratory Medicine, Inje University College of Medicine, Busan Paik Hospital 633-165, Gaegum-dong, Busanjin-gu, Busan 614-735, Korea Tel: ＋82-51-890-6862, Fax: ＋82-51-893-1562 E-mail: jeong418@medimail.co.kr

Received 26 February 2009 Revised 1 June 2009 Accepted 5 June 2009

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

Activating mutations of the fms-like tyrosine kinase 3 gene (FLT3) by internal tandem duplication (ITD) in the juxtamembrane region are found in 20∼30% of the adults with acute myeloid leukemia (AML). The allelic ratio of FLT3/ITD (ITD-AR), as assessed by Genescan analysis, has been reported to carry prognostic significance in AML patients who have normal karyotype.

Methods

FLT3/ITD was studied by PCR in 113 adults with AML including 55 patients with normal karyotype. Genescan analysis was performed for the PCR products to determine the allelic distribution. The results were correlated with the prognostic factors.

Results

FLT3/ITD was found in 23% of the total AML patients and in 32.7% of those patients with normal karyotype. The mutation was related to a high WBC count, a high serum LD level and a low percentage of CD34 positive cells. The ITD-AR ranged from 0.05 to 8.27 (median, 0.61). The patients with a high ITD-AR (≥0.7) had significantly higher WBC count and LD level than those without FLT3/ITD. On multivariate analysis, a high ITD-AR as well as FLT3/ITD were confirmed to be independent adverse prognostic factors for AML patients with normal karyotype.

Conclusion

This study demonstrated that a high ITD-AR and FLT3/ITD had major adverse impacts on the prognostic relevance for AML patients with normal karyotype.

Keywords: Acute myeloid leukemia, Normal karyotype, FLT3 internal tandem duplication

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Fig. 1.

Genescan analysis of FLT3/ITD levels in AML patients. (A) wild type of FLT3 gene, (B∼D) wild type and various size of ITD in FLT3 gene. Abbreviations: FLT3, fms-like tyrosine kinase; ITD, internal tandem duplication; AML, acute myeloid leukemia.

Table 1.

Clinical characteristics of total AML patients including patients with FLT3/ITD and distribution of patients with FLT3/ITD

Characteristics	Total patients	FLT3/ITD
No. of cases	113	26
Age (yr, median)	20∼85 (51)	20∼80 (54)
Male：Female	55：58	13：13
FAB subgroup (de novo, N)
M0	8	1
M1	32	8
M2	41	7
M3	21	6
M4e	5	2
M5	2	1
M6	0	0
M7	1	0
Unclassified∗	2	1
Secondary AML	1	0

^∗ Bone marrow aspiration is inadequate for FAB classification of AML because of dry tap. Abbreviations: FLT3/ITD, fms-like tyrosine kinase internal tandem duplication; AML, acute myeloid leukemia.

Table 2.

Cytogenetic classification of total AML patients including patients with FLT3/ITD and distribution of patients with FLT3/ITD

Cytogenetic prognostic group	Total	FLT3/ITD
Cytogenetic prognostic group	patients	N	%
Favorable	32	6	18.8
t(8;21)	12	2	16.7
t(15;17)	16	3	18.8
inv(16)/t(16;16)	4	1	25.0
Intermediate∗	71	20	28.8
Normal karyotype	52	17	32.7
Numerical aberration	11	3	27.3
Balanced structural rearrangement	2	0	0.0
Unbalanced structural rearrangement	6	0	0.0
Unfavorable	10	0	0.0
?7	5	0	0.0
Complex chromosomal abnormalities	2	0	0.0
Others^†	3	0	0.0

^∗ Numerical aberration, +8, +11, +21, ?X, ?Y; Balanced structural rearrangement, t(1;19), t(7;11); Unbalanced structural rearrangement, add(1p), del(9q), del(12q), del(15q), del(17q), der(14q). ^†Others are included in t(3;3), del(11) (q23).

Table 3.

Genescan analysis in patients with FLT3/ITD

No.	Allele	FLT3/ITD ratio (mutant/wild)
1	329–393	0.06
2	329–335	0.10
3	329–386	0.18
4	329–402	0.19
5	329–384	0.21
6	329–353	0.31
7	329–379	0.38
8	329–382	0.43
9	329–350	0.50
10	329–376	0.54
11	329–373	0.60
12	329–356	0.60
13	329–350	0.61
14	329–439	0.61
15	329–384	0.70
16	329–411	0.72
17	329–382	0.72
18	329–370	0.72
19	329–390	0.72
20	329–373	0.74
21	329–344–347	0.78
22	329–344	0.83
23	329–353	0.89
24	329–382	1.12
25	329–350	1.44
26	329–353–382	8.27
27∗	329–350	1.71
28∗	329–382	3.20

^∗ Results from the patients with FLT3/ITD in relapse of AML.

Table 4.

Characteristics according to FLT3/ITD status in AML patients with normal karyotype

Characteristics	Total patients	FLT3/ITD positive	FLT3/ITD negative	P
No. of cases	52	17	35
Male：Female	24：28	9：8	15：20	0.44
Age _(yr, _median)	55	60	54	0.36
Range	(20∼80)	(20∼80)	(22∼79)
WBC count (×10⁹/L, median)	16.2	67.3	12.9	0.003
Range	(0.4∼349.9)	(2.0∼349.9)	(0.4∼204.3)
LD level (U/L, median)	1,039	1,780	706	0.003
Range	(305∼5,401)	(388∼5,401)	(305∼3,179)
Bone marrow blasts (%, median)	78.2	86.0	74.7	0.56
Range	(21.5∼96.3)	(21.5∼94.3)	(27.2∼96.3)
CD34+ cells (%, median)	44.5	20.1	84.6	0.005
Range	(0.03∼99.4)	(0.03∼68.1)	(0.06∼99.4)

Abbreviation: LD, lactate dehydrogenase.

Table 5.

Comparison of ch haracteristics of AML patients with high, low ITD-AR, or ITD wild typ pe

Characteristics	ITD wild type	Low ITD-AR (＜0.7)	High ITD-AR (≥0.7)		P
Characteristics	ITD wild type	Low ITD-AR (＜0.7)	High ITD-AR (≥0.7)	Wild vs low	Wild vs high	Low vs high
No. of cases	87	14	12
Age _(yr, _median)	49	48	55	0.5	0.36	0.9
Range	(22∼85)	(26∼80)	(20∼67)
WBC count (×10⁹/L, median)	10.3	38.6	93.9	0.01	＜0.0001	0.07
Range	(0.2∼204.3)	(4.0∼195.2)	(2.0∼349.9)
LD level (U/L, median)	765	1,255	2,055	0.09	＜0.0001	0.1
Range	(286∼9,319)	(338∼6,255)	(709∼5,401)
BM blasts (%, median)	71.1	84.7	81	0.46	0.74	0.86
Range	(0.6∼96.6)	(34.6∼94.3)	(2.7∼91.9)
BM CD34+ cells (%, median)	80.5	35.2	35	0.41	0.05	0.82
Range	(0.06∼99.7)	(0.03∼98.4)	(0.58∼61.3)

Abbreviation: ITD-AR, internal tandem duplication allelic ratio.

Table 6.

Results of Cox regression analysis of survival in AML patients with normal karyotype

Variable	Overall survival			Disease free survival
Variable	Hazard ratio	95% CI	P	Hazard ratio	95% CI	P
FLT3/ITD	0.233	0.054∼1.000	0.051	0.321	0.060∼1.717	0.186
ITD-AR (≥0.7)	3.012	1.274∼7.119	0.012	3.505	1.049∼11.706	0.042

Abbreviation: CI, confidence interval.

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