Expires July 2024
Diagnosis of myelodysplastic syndrome and other myeloid neoplasms requires correlation of clinical, morphologic, and cytogenetic findings, but flow cytometric immunophenotyping method can be useful in assessing myeloid dysmaturation. Dragan Jevremovic, M.D., Ph.D., describes a new flow cytometric test to detect aberrant patterns of expression in the diagnosis of myelodysplastic syndrome.
Dragan Jevremovic, M.D., Ph.D., Co-Director of the Cell Kinetics Laboratory at Mayo Clinic in Rochester, Minn.
Our speaker for this program is Dr. Dragan Jevremovic, Co-Director of the Cell Kinetics Laboratory at Mayo Clinic in Rochester MN. Dr. Jevremovic describes the use of flow cytometric analysis of bone marrow for the presence of dysplasia in chronic myeloid neoplasms.Welcome to Mayo Medical Laboratories Hot Topics. These presentations provide short discussion of current topics and may be helpful to you in your practice.
As you view this presentation, consider the following important points regarding Myeloid Blast and Maturation Assessment by Flow Cytometry.
Dr. Jevremovic thank you for presenting with us today.
Thanks for the introduction, I have nothing to disclose.
Chronic myeloid neoplasms are a group of disorders that affect hematopoietic stem cells and are more frequent in adults and older patients. They can be broadly divided into myelodysplastic syndrome or MDS, myeloproliferative neoplasms or MPN, and neoplasms with mixed dysplastic and proliferative features or MDS/MPN. MDS is characterized by block in differentiation of hematopoietic precursors, leading to cytopenias and propensity to develop acute myeloid leukemia. Myeloproliferative neoplasms usually have increased peripheral blood counts, with hypercellular marrow and marrow fibrosis.
WHO classification of hematologic neoplasms from 2008 defines MDS based on clinical presentation, morphologic features of cells, blast counts, and cytogenetic and molecular genetic findings. Potential role of flow cytometry immunophenotyping in the diagnosis of MDS is also mentioned.
Since approximately 15 to 20 years ago, many studies have shown correlation of flow cytometry findings with presence of dysplasia defined by morphologic or cytogenetic findings. These studies can be divided into quantitative and qualitative. In quantitative studies, there is a set ratio of cell population counts, or ratios of quantitative expression of antigens and side scatters on different cell populations. For these approaches, careful instrument settings and strict staining procedures are necessary. Recently, some of these quantitative studies have utilized software for automatic gating of different cell populations and multidimensional evaluation of population attributes. In contrast, qualitative studies depend on the operator recognition of specific pattern of expression on 2-dimensional dot plots. While qualitative studies are less sensitive to instrument settings and staining procedures, they require operator training in order to recognize normal and abnormal antigen expression patterns.
For all the reasons mentioned, flow cytometry as a diagnostic modality for MDS and other chronic myeloid neoplasms has been difficult to standardize between laboratories. In addition, most studies were performed by comparing normal with dysplastic bone marrows, without including the spectrum of atypical specimens which are usually seen in the routine practice. For that reason, WHO 2008 classification stated that cases with evidence of dysplasia by flow cytometry only, should be reevaluated, essentially stating that flow cytometry is only an adjunct diagnostic modality for detection of dysplasia.
Here at Mayo Clinic, we have developed a flow cytometry test for myeloid dysplasia on bone marrow aspirates, that is based on experience of our laboratory and many others. The panel of antibodies used in 2 tubes is the same as our acute panel, and includes CD2, CD7, CD13, CD15, CD33, CD34, CD36, CD56, CD64, CD45, CD117, and HLA-DR. Our test is qualitative and requires interpretation of patterns of expression of antigens, primarily on myeloid blasts, but also examines maturing granulocytic population. Aberrant patterns of antigen expression can be seen in MDS and in a smaller percentage of myeloproliferative and mixed myelodysplastic/myeloproliferative neoplasms.
Our assessment of myeloid precursors is based on 3 parameters. First, we examine the expression of CD13 and HLA-DR on the population of CD34-positive blasts. As can be seen in this slide, normal CD34-positive blasts show a specific pattern of CD13/HLA-DR expression with 3 readily recognizable populations. This heterogeneity of blasts is lost in majority of MDS cases, as shown in the lower part of the slide.
Our second parameter is examination of CD2, CD7, and CD56 on CD34-positive blasts. Normal myeloid blasts are negative for these antigens, while a subset of myeloid neoplasms shows aberrant coexpression of one or all of these markers, as shown in the lower panel. In this example, abnormal CD34-positive blasts show uniform expression of CD56 and partial expression of CD7.
The third parameter for assessing dysplasia by flow cytometry is maturation pattern of granulocytes on CD13/CD16 plot. Normal granulocytes show sequential progression from promyelocytes in teal color which are CD13 positive CD16-negative, through yellow immature granulocytes showing negativity for both CD13 and CD16, to finally blue mature CD13- and CD16-positive neutrophils. This pattern of normal maturation, shown in the upper panel, is lost in a subset of MDS cases, as shown is the lower panel.
The results of our studies are interpreted as normal, atypical or aberrant. We decided to err on the side of caution and sacrifice some sensitivity in order to make sure that we don’t overcall aberrant findings. Our sensitivity and specificity are approximately 70 and 95%, respectively. More details on our approach can be found in a recent publication in American Journal of Clinical Pathology.
As WHO 2008 classification suggests, all flow cytometry findings should be correlated with clinical, morphologic, and cytogenetic findings before diagnosing myeloid neoplasm. In addition, per our internal algorithm, we will perform the triage panel containing CD3, CD10, CD16, CD19, CD34, CD45, kappa, and lambda on every ordered myeloid flow. It is not uncommon to find a B-cell clone or large granular lymphocyte population in patients presenting with cytopenia and suspected MDS.
In summary, our new flow cytometry test examines myeloid maturation on bone marrow specimens. The test includes the triage panel and there is no need to order it separately. The findings are interpreted as normal, atypical and aberrant. Correlation with clinical, morphologic and cytogenetic findings is necessary in order to diagnose myeloid neoplasm.