Can threshold for MPO by flow cytometry be reduced in classifying acute leukaemia? A comparison of flow cytometric and cytochemical myeloperoxidase using different flow cytometric cut-offs

Current Status of Flow Cytometric Immunophenotyping of Hematolymphoid Neoplasms in Korea

Background

Flow cytometric immunophenotyping of hematolymphoid neoplasms (FCI-HLN) is essential for diagnosis, classification, and minimal residual disease (MRD) monitoring. FCI-HLN is typically performed using in-house protocols, raising the need for standardization. Therefore, we surveyed the current status of FCI-HLN in Korea to obtain fundamental data for quality improvement and standardization.

Methods

Eight university hospitals actively conducting FCI-HLN participated in our survey. We analyzed responses to a questionnaire that included inquiries regarding test items, reagent antibodies (RAs), fluorophores, sample amounts (SAs), reagent antibody amounts (RAAs), acquisition cell number (ACN), isotype control (IC) usage, positive/negative criteria, and reporting.

Results

Most hospitals used acute HLN, chronic HLN, plasma cell neoplasm (PCN), and MRD panels. The numbers of RAs were heterogeneous, with a maximum of 32, 26, 12, 14, and 10 antibodies used for acute HLN, chronic HLN, PCN, ALL-MRD, and multiple myeloma-MRD, respectively. The number of fluorophores ranged from 4 to 10. RAs, SAs, RAAs, and ACN were diverse. Most hospitals used a positive criterion of 20%, whereas one used 10% for acute and chronic HLN panels. Five hospitals used ICs for the negative criterion. Positive/negative assignments, percentages, and general opinions were commonly reported. In MRD reporting, the limit of detection and lower limit of quantification were included.

Conclusions

This is the first comprehensive study on the current status of FCI-HLN in Korea, confirming the high heterogeneity and complexity of FCI-HLN practices. Standardization of FCI-HLN is urgently needed. The findings provide a reference for establishing standard FCI-HLN guidelines.

Update on Acute Leukemias of Ambiguous Lineage

Acute leukemias of ambiguous lineage are a heterogenous group of diseases that include acute undifferentiated leukemias and mixed-phenotype acute leukemias (MPALs). These leukemias pose a challenge for pathologists and clinicians alike in diagnosis, treatment, and further management. Recent genetic characterization has provided insights into their underlying biology and classification, and has offered potential for targeted therapies. This article addresses diagnosis of MPALs with examples of the most common pitfalls, recent comprehensive molecular studies, and advancement in treatment and follow-up modalities.

Standardised immunophenotypic analysis of myeloperoxidase in acute leukaemia

Given its myeloid‐restricted expression, myeloperoxidase (MPO) is typically used for lineage assignment (myeloid vs. lymphoid) during acute leukaemia (AL) diagnostics. In the present study, a robust flow cytometric definition for MPO positivity was established based on the standardised EuroFlow protocols, the standardised Acute Leukaemia Orientation Tube and 1734 multicentre AL cases (with confirmed assay stability). The best diagnostic performance was achieved by defining MPO positivity as ≥20% of the AL cells exceeding a lymphocyte‐based threshold. The methodology employed should be applicable to any form of standardised flow cytometry.

International cooperative study identifies treatment strategy in childhood ambiguous lineage leukemia

Despite attempts to improve the definitions of ambiguous lineage leukemia (ALAL) during the last 2 decades, general therapy recommendations are missing. Herein, we report a large cohort of children with ALAL and propose a treatment strategy. A retrospective multinational study (International Berlin-Frankfurt-Münster Study of Leukemias of Ambiguous Lineage [iBFM-AMBI2012]) of 233 cases of pediatric ALAL patients is presented. Survival statistics were used to compare the prognosis of subsets and types of treatment. Five-year event-free survival (EFS) of patients with acute lymphoblastic leukemia (ALL)-type primary therapy (80% ± 4%) was superior to that of children who received acute myeloid leukemia (AML)-type or combined-type treatment (36% ± 7.2% and 50% ± 12%, respectively). When ALL- or AML-specific gene fusions were excluded, 5-year EFS of CD19⁺ leukemia was 83% ± 5.3% on ALL-type primary treatment compared with 0% ± 0% and 28% ± 14% on AML-type and combined-type primary treatment, respectively. Superiority of ALL-type treatment was documented in single-population mixed phenotype ALAL (using World Health Organization and/or European Group for Immunophenotyping of Leukemia definitions) and bilineal ALAL. Treatment with ALL-type protocols is recommended for the majority of pediatric patients with ALAL, including cases with CD19⁺ ALAL. AML-type treatment is preferred in a minority of ALAL cases with CD19^- and no other lymphoid features. No overall benefit of transplantation was documented, and it could be introduced in some patients with a poor response to treatment. As no clear indicator was found for a change in treatment type, this is to be considered only in cases with ≥5% blasts after remission induction. The results provide a basis for a prospective trial.

Comparison of Immunohistochemistry, Cytochemistry, and Flow Cytometry in AML for Myeloperoxidase Detection

Acute Myeloid Leukemia (AML) as per World Health Organization (WHO 2008) classification is on the basis of the antigenic characterization, enzymes restriction in the neoplastic myeloid cells and the specific translocations/mutations. AML can be assessed and differentiated by flowcytometry (FCM)/immunohistochemistry (IHC)/cytochemistry techniques. Myeloperoxidase (MPO) is an unequivocal marker to differentiate AML from the acute lymphoblastic leukemia. Despite FCM popularity, it has its limitations, in form of 'dry-tap', cost, and inability of being performed by retrospective analysis. IHC, though an old technique has overcome these disadvantages of FCM. Cytochemistry, on the other hand has its own advantages in being cost-effective; technically easy to do while its disadvantages are its inability to be carried out in the old samples, 'dry-tap' conditions in aleukemic leukemia. There has been non-uniformity in the literature among these techniques especially concerning their sensitivity for MPO. A prospective study was done at All India Institute of Medical Sciences New Delhi from 01 July 2014 to 30 Nov 2015 to include 120 diagnosed acute myeloid leukemia cases. Myeloperoxidase stain was done by cytochemistry, immunohistochemistry and flow cytometry and results were compared. There were 28 cases which showed discrepancies. Out of these 28 cases immunohistochemistry showed positivity in majority (22 cases) followed by flow cytometry (14 cases). Therefore it is important to employ more than one technique and IHC must be included for detection of MPO in all suspected cases of AML especially when negative with FCM .

Importance of CD117 in the Assignation of a Myeloid Lineage in Acute Leukemias

The correct classification of acute leukemias (AL) is an essential part in the evaluation of any patient with this disease. Historically, CD117 has been an important asset in the diagnosis of patients with mixed-phenotype acute leukemia (MPAL). In an attempt to simplify the diagnosis of MPAL with fewer and more lineage specific markers, the World Health Organization (WHO) proposed in 2008 a new criteria for the diagnosis of this type of AL, which excluded CD117 from the myeloid markers that are utilized to diagnose MPAL. In order to assess whether CD117 is necessary in the diagnosis of MPAL, we evaluated the sensitivity and specificity of CD117 for acute myeloid leukemia (AML) in 331 patients with AL. The calculated sensitivity of CD117 for AML was 85.88% (103/120), while the specificity was 83.9% (177/211). Besides myeloperoxidase (MPO), which was used as the gold standard in differentiating AML from other type of ALs, the most specific markers for AML in our study were CD14 and CD64 (99.5 and 95.6%). Although the specificity of CD117 in this study is not as high as CD14 and CD64, markers concomitantly used in this this study and in the WHO classification, based on the results of other researches (i.e. the specificity of CD117 for AML was 100% in one study) and due to the fact that its specificity for AML in this study is relatively high, we recommend the use CD117 in assigning a myeloid lineage in MPAL.

[Expression of cMPO in 502 cases of acute myeloid leukemia (AML) and its diagnosis significance in AML subtypes]

目的

探讨髓过氧化物酶（cMPO）在急性髓系白血病（AML）患者中的表达及其在诊断分型中的意义。

方法

采用CD45/SSC双参数散点图设门方法对502例AML患者进行八色流式细胞术免疫表型分析，观察患者白血病细胞cMPO表达的阳性率和阳性强度。

结果

502例AML患者cMPO总体阳性率为58.0%，其中阳性占21.5%，弱阳性占34.1%，部分阳性占2.4%；阴性占42.0%。各亚型中，AML伴t(15;17）（q22;q12）/PML-RARα的cMPO阳性率最高，为100%，阳性强度多数接近正常粒细胞水平；其次为AML伴t(8;21）（q22;q22）/RUNX1-RUNX1T1，阳性率为91.4%，阳性强度多为弱阳性；AML微分化型和急性巨核细胞白血病患者cMPO表达皆为阴性；余各亚型阳性率在22.7%~76.2%。

结论

各亚型AML cMPO的阳性率及阳性强度存在显著差异。