Flow Cytometric Analysis in Myelodysplastic Syndrome (MDS).

The MDS are heterogeneous clonal stem cell disorders. Dysplastic changes in morphology and functional abnormalities in multiple cell lines precede leukemic transformation in most patients. An abnormal immunophenotype has been identified in some hematopoetic clonal disorders on flow cytometric analysis. However, no clear immunophenotypic aberrancies, such as loss of differentiation or cross expression of markers of different lineages, have been described in MDS. We performed this retrospective analysis to identify an immunophenotypic signature distinguishing MDS from secondary causes of cytopenia on flow cytometric analysis. Data were reviewed for patients who had bone marrow aspirate and biopsy performed at our institution from 2000 to 2004 for evaluation of cytopenias or dysplasia in peripheral blood. Patients who had a non-MDS hematological malignancy, other neoplasms involving the bone marrow, or cytopenias secondary to chemotherapy were excluded. Flow cytometry was done on unfractionated bone marrow aspirates using a standardized panel including CD5, CD10, CD34, CD11c, CD117, CD19, CD20, CD22, CD14, CD56, CD33, CD13, CD2, CD8, CD4, CD3, CD7, CD24, CD16, kappa, and lambda antibodies. Ten of 93 cases were found to have a non-MDS malignant disorder or chemotherapy induced cytopenia and were excluded from analysis. Of the remaining 83 cases, MDS was diagnosed based on morphology and cytogenetic findings in 29 cases. Twenty-one patients had refractory anemia (RA), one had RA with ringed sideroblasts, six had RA with excess of blasts and one had treatment related MDS. The remaining patients had cytopenias secondary to infection, peripheral consumption, inflammation, autoimmune disease or medications. The median age was 74 for the MDS group and 54 for non-MDS group. Data for International Prognostic Scoring System (IPSS) was available for 17 patients. Three had a low IPSS, 5 were Intermediate-1, 6 were Intermediate-2, and 3 were high. Flow cytometric immunophenotyping was useful in characterizing and enumerating myeloblasts in the blast gate (CD45 dim positive/negative, low complexity side scatter) in all patients with RAEB (n=6). Interestingly, aberrant CD34 expression was seen in a fraction of cells in the neutrophil gate (CD45 bright positive, high complexity side scatter) in six patients (20.6%) with refractory anemia with no blasts morphologically. This feature was not present in the non-MDS group (P<0.01). However, loss of CD10 expression on myelomonocytic cells was seen in four MDS patients (14.8%) and in 2 non-MDS patients (3.2%) (P=0.1). No other aberrant phenotypic pattern clearly distinguished between the MDS and non-MDS groups. An increased number (>10% in the lymphocyte gate) of CD56 and CD2 positive NK cells was seen in both groups (44.8% of MDS group and 40.7% of non-MDS). In conclusion, flow cytometric analysis may be useful in characterization and enumeration of blasts in RAEB. Although no consistent, characteristic immunophenotypic abnormalities were identified, expression of CD34 and loss of CD10 on dysplastic granulocytes in the bone marrow of a subset of patients with MDS may represent asynchronous expression of immunophenotypic markers suggestive of arrest in differentiation and warrants further exploration.