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 Table of Contents  
ORIGINAL ARTICLE
Year : 2019  |  Volume : 44  |  Issue : 1  |  Page : 48-53

CD34 expression and FLT3 mutation are independent poor prognostic factors in normal karyotype acute myeloid leukemia


Haematology Unit, Internal Medicine Department, Zagazig University Hospitals, Zagazig, Egypt

Date of Submission16-Dec-2018
Date of Acceptance31-Jan-2019
Date of Web Publication27-Sep-2019

Correspondence Address:
Ahmed Y Amer
24 Furness Avenue, Blackpool FY3 7QQ, UK
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ejh.ejh_51_18

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  Abstract 


Background The prognostic impact of CD34 expression on malignant myeloid leukemia blast cells is still under debate. FLT3 mutation is a well-known poor prognostic factor in acute myeloid leukemia (AML). The aim of the study was to assess CD34 expression in this subgroup of AML patients to detect the association of CD34 expression with FLT3-internal tandem duplication (ITD) mutation and its impact on the outcome.
Patients and methods This prospective study, carried out at Zagazig University Hospitals, included 33 de-novo AML patients with a normal karyotype. CD 34 expression was detected by flow cytometry using FITC florescent monoclonal antibody and it was considered positive if a cutoff level of 10% expression was exceeded. FLT3-ITD mutation was detected by PCR.
Results CD34 was positive in 20 cases while 13 cases were negative. Twenty-one cases were FLT3-ITD wild type while 12 cases were mutated. FLT3 mutation was significantly linked to CD34 reactivity (P=0.048). CD34-positive cases were associated with a significantly less complete remission (CR) achievement rate (33 and 80% in CD34-positive and CD34 negative, respectively, P=0.03). Those with positive CD34 had significantly lower overall survival compared with CD34-negative cases. Multivariate cox regression survival analysis showed that positive CD34 was a predictor of poor survival and higher risk of mortality (HR=1.3 and P=0.027, confidence interval, 1.1–2.9).
Conclusion CD34 expression is a poor prognostic biomarker in normal karyotype AML. It is associated with and further worsens the poor prognosis in FLT3-mutated cases. Its role in different subgroups of AML layered by different genetic aberrations needs further study.

Keywords: acute myeloid leukemia, CD34, FLT3, normal cytogenetics, normal karyotype, prognostic


How to cite this article:
Elakkad MA, Abdelhalim AF, Salah HE, Amer AY. CD34 expression and FLT3 mutation are independent poor prognostic factors in normal karyotype acute myeloid leukemia. Egypt J Haematol 2019;44:48-53

How to cite this URL:
Elakkad MA, Abdelhalim AF, Salah HE, Amer AY. CD34 expression and FLT3 mutation are independent poor prognostic factors in normal karyotype acute myeloid leukemia. Egypt J Haematol [serial online] 2019 [cited 2019 Oct 23];44:48-53. Available from: http://www.ehj.eg.net/text.asp?2019/44/1/48/268009




  Introduction Top


Acute myeloid leukemia (AML) is a malignancy of primitive blood-forming cells of the bone marrow characterized by defective proliferation and differentiation functions of hematopoietic precursor cells with subsequent accumulation of these cells and depression of normal hematopoiesis [1]. It accounts for about 80% of acute leukemia in adults and 20% of acute leukemia in pediatrics [2].

The prognosis of AML patients varies greatly, ranging from short survival of few days to complete cure. The outcome can be in part predicted by age, performance status, and cytogenetics [3],[4],[5].

CD34 is a surface marker that was described for the first time by Civin et al. [6] as a cell-surface glycoprotein. It has as a cell-to-cell adhesion promotor function [7]. It may play a role as a mediator of attachment of bone marrow stem cells to bone marrow extracellular matrix or directly to stromal cells [8],[9].

The prognostic role of CD34 was extensively studied in the late 1980s and 1990s. It has been identified as an adverse prognostic marker in many studies [10],[11],[12],[13],[14]. On the other hand, other studies contradicted these conclusions doubting any significant prognostic value of CD34 [15],[16],[17],[18],[19],[20],[21]. Owing to this controversy, CD34 expression was considered not to be of value as a prognostic marker by Kanda et al. [22] who conducted a meta-analysis of data of 2483 patients from 22 studies.

In the current era of expanding understanding of cytogenetics and gene mutations involved in the pathogenesis of AML and its great impact on prognosis and management, CD34 has been reinvestigated to detect its significance in the light of these factors, for example FLT3, CEBPA, NPM1 mutation status, and different chromosomal aberrations [23],[24],[25].

FMS-like tyrosine kinase 3 is a transmembrane tyrosine kinase receptor which stimulates cell proliferation upon activation. Mutations in the FLT3 gene, producing internal tandem duplications (FLT3-ITD) and activation of the FLT3 receptor tyrosine kinase, are common in AML, especially in patients with normal karyotypes. It has been associated with worse outcome in AML patients receiving intensive chemotherapy [26]. FLT3-ITD mutational status is the main predictor of outcome in patients with intermediate-risk AML [27].

This study aimed to assess CD34 expression in AML patients with a normal karyotype together with FLT3-ITD to detect the association of CD34 expression and FLT3-ITD mutation and their impact on the outcome.


  Patients and methods Top


This prospective study had been carried out at the Haematology Unit, Internal Medicine Department, Zagazig University Hospital and it included 33 de-novo AML patients with normal karyotypes. this study was approved by IRB, faculty of medicine zagazig university on 8/1/2017, IRB#: 3319/8-1-17. written consent was given by all participants. All adult normal karyotype AML patients of both sexes above 18 years of age with normal liver and renal functions and good PS were included. All patients had given their informed consent. All patients having severe cardiac, pulmonary, hepatic, renal, neurological, metabolic disease, or concomitant malignancies were excluded from the study. All patients were subjected to thorough history and physical examination, basic laboratory investigations including complete blood counts, liver and kidney functions, serum electrolytes, coagulation profile, hepatitis B surface antigen, hepatitis C antibody, HIV antibody, and bone marrow aspiration. Immunophenotyping of EDTA bone marrow sample was performed on Becton Dickinson BD (San Diego, CA, USA), FAC scan flow cytometer using acute leukemia panel (CD33, CD34, MPO, CD5, CD3, TDT, CD10, CD13, CD14, CD7, CD19, CD20, CD22, CD64, CD79a, HLA-DR) using a panel of fluorescein (FITC) and phycoerythrin conjugated MoAbs reactive with these antigens. Detection of CD34 expression by flow cytometry on malignant myeloid cells of bone marrow aspirate used FITC florescent monoclonal antibody and it was considered positive if a cutoff level of 10% expression was exceeded. Conventional cytogenetic study was done for all patients. PCR for FLT3 mutation was done for all patients.

All these patients were treated by induction 3 and 7 chemotherapy protocols, that is 3 days of adriamycin 25 mg/m2 and 7 days of continuous infusion of cytarabine 100 mg/m2. Bone marrow aspirate evaluation was carried out at day 14 of end of induction protocol. Response was assessed according to standardized international response criteria.

After achievement of remission, patients with FLT3 mutation were classified as of unfavorable risk and were considered for Haematopoietic stem cell transplantation (HSCT). Those with FLT3 wild type were challenged for consolidation of high-dose chemotherapy regimens such as HAM, that is high-dose Ara C 1.5 g/m2/12 h days 1–3, mitoxantrone 12 mg/m2 days 3–5 for four cycles, and then follow-up.

Patients were followed up 3 monthly after end of the treatment for a median follow-up period of 20 months. The follow up included physical examination and complete blood picture Bone marrow examination was done every 3–6 months unless a suspicious complete blood count result or clinical data warranted earlier assessment.

Statistical analysis

The collected data were computerized and statistically analyzed using SPSS program, version 24 (IBM, New York, USA). Data were tested for normal distribution using the Shapiro–Walk test. Qualitative data were represented as frequencies and relative percentages. χ2 test and Fisher’s exact were used to calculate the difference between qualitative variables as indicated. Qualitative data were compared by independent t test. All statistical comparisons were two tailed with a significance level of P value less than or equal to 0.05 indicating statistical significance. Kaplan–Meier method was used to estimate overall and disease-free survival and log-rank test compared survival curves (P value was considered significant at ≤0.05 levels).


  Results Top


Our study included 33 de-novo AML patients. Their clinical and demographic characteristics are summarized in [Table 1].
Table 1 Clinical and demographic characteristics of the studied group

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CD34 was positive in 20 (61%) cases while 13 (39%) cases were negative. Twenty-one (66%) cases were FLT3-ITD wild type, while 12 (about 34%) cases were mutated. FLT3 mutation was significantly linked to CD34 reactivity (P=0.048) ([Table 2]). CD34-positive cases were associated with a significantly less complete remission (CR) achievement rate (33 and 80% in CD34 positive and CD34 negative, respectively, P=0.03). This was exactly the same with FLT3-ITD mutant cases (9 and 66% in FLT3 mutant and wild type, respectively, P=0.004).
Table 2 Association between CD34 expression status with FLT-internal tandem duplication mutation

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The impact of CD34 expression and FLT3-ITD mutation status on the overall survival and disease-free survival has been examined using the Kaplan–Meier log survival function. It showed that those with positive CD34 had significantly lower overall survival compared with CD34-negative cases (10.2 vs. 15.7 months with P=0.01). Combining CD34 expression and FLT3-ITD mutation status results showed that CD34 positivity further worsened the already worse prognosis of FLT3-ITD-mutated AML cases indicating that it is an independent risk factor in this group ([Figure 1] and [Figure 2]). The mean overall survival for each group is shown in [Table 3]. Multivariate cox regression survival analysis was used to assess if CD34 poor prognostic value on overall survival is independent of other prognostic factors in AML ([Table 4]). Positive CD34 was a predictor of poor survival and higher risk of mortality (HR=1.3 and P=0.027; confidence interval, 1.1–2.9).
Figure 1 Correlation between overall survival and CD34 expression/FLT3-ITD mutation status. ITD, internal tandem duplications.

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Figure 2 Correlation between DFS survival and CD34 expression/FLT3-ITD mutation status. ITD, internal tandem duplications.

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Table 3 Correlation between overall survival and CD34 expression/FLT3-internal tandem duplication mutation status

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Table 4 Univariate and multivariate cox regression analyses of different prognostic factors for overall survival

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  Discussion Top


In our work, we defined CD34 positivity by a cutoff value of 10% of examined cellular population by flow cytometry. Most of previous studies used a 20% cutoff. However, Schuurhuis and colleagues have claimed that the true negative CD34 AML is only defined with a lower than 1% of CD34 expressing population. Using this cutoff for defining truly negative AML is associated with a significantly better outcome. They claim that excluding such cases from analysis leaves no prognostic value for CD34 [28].

Zeijlemaker and colleagues used a new definition, without using prior cutoff. This definition used the presence or absence of neoplastic CD34-positive cells, which appears to be a powerful predictor for event free survival (EFS) and overall survival (OS) in the entire group of AML patients. Therefore, this new definition not only explains conflicting results published in the past, but also indicates that this independent prognostic marker should be incorporated into AML risk stratification [29].

Twenty (61%) of the studied AML patients had a positive CD34 while only 13 (39%) cases were CD34 negative. According to Raspadori et al. [10], 47% of the AML patients were CD34 negative. Most of the studies that examined CD34 expression were near these but as this study examines CD34 in a different population (subgroup of AML cases), this can explain this difference.

In our study, we examined 33 patients of normal karyotype for FLT3-ITD mutation. Twenty-one cases of them were wild while 12 (about 34%) cases were mutated. This is very similar to what Ebrahim et al. [25] had found 35%. In our study 10/12 FLT3-mutated cases were CD34 positive while 10/21 cases of wild FLT3 were CD34 positive with a P value of 0.045. This is consistent with the findings of Ebrahim et al. [25] and Pollard et al. [30].

In our work, 15/33 (45%) patients achieved remission. Those with negative CD34 had significantly higher CR rate than CD34-positive cases (80 and 33%, respectively) with a P value of 0.03. These were close to the results from Geller et al. [31] (87 and 59%, respectively). However, according to Zeijlemaker et al. [29] this was 67 and 58%, respectively.

Survival analysis for our patients showed that those with positive CD34 had significantly lower overall survival compared with CD34-negative cases (10.2 vs. 15.7 months with P=0.01). Same results were identified for disease-free survival (5.9 vs. 12.3 months with P=0.002). These results are consistent with the data from many studies [10],[11],[12],[13],[14]. However, it contradicts results from other studies [15],[16],[17],[18],[19],[20],[21]. Reasons for these discrepancies include specimen analyzed (bone marrow or peripheral blood), erythrocyte-lysed whole blood versus gradient density mononuclear cell fractions, use of cryopreserved versus fresh samples, detection systems employed (flow cytometry, immunofluorescence microscope, immune-enzymatic technique), use of different CD34 antibodies recognizing distinct CD34 epitopes (classes I, II, III), degree of intensity for CD34 antigen, cutoff levels for the discrimination of positive and negative cases (5–20%, percentage of leukemic cells present in the sample examined), patients analyzed [de-novo or secondary AML; childhood or adult acute lymphoblastic leukaemia (ALL)], biologic characteristics of acute leukemic cells (chromosome or gene abnormalities), and lastly the type of chemotherapy regimen used [32].

To examine the effect of CD34 expression on the outcome in FLT3-mutated versus wild cases, we compared the overall and disease-free survival of four groups based on both CD34 expression and FLT3 mutation status. Those with wild-type FLT3 and negative CD34 (11 cases) had the best outcome with 16.9 months overall survival and 11.8 months of disease-free survival (P=0.0005), while those with CD34-positive expression and mutated FLT3 (10 cases) the mean overall survival was 5.4 months and the disease-free survival was only 1.7 months. These results typically match the results of Ebrahim et al. [25] as well as the results from Schuurhuis et al. [28].

Finally, multivariate cox regression model examined the impact of CD34 on overall survival with other prognostic factors to test its independent prognostic effect. It showed quite clearly that CD34 positivity is associated with higher mortality rates and poorer outcome independent of all other risk factors (HR=1.3 and P=0.027; confidence interval, 1.1–2.9). This is consistent with what Ebrahim et al. [25] has proved in their study.


  Conclusion Top


Positive CD34 is a marker for less CR achievement. CD34 is associated with FLT3-ITD mutation and is an independent factor for worse outcome in this patient group.

Recommendation

More studies are strongly needed to investigate the function of CD34 in AML. As the role of gene mutations and chromosomal aberrations in subclassifying AML is expanding, extensive studies of these AML subtypes based on their cytogenetics and role of CD34 and other immunophenotypes in identifying these subgroups and their prognostication is highly recommended.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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