PB2082 PHENOTYPIC ALTERATIONS IN CHRONIC MYELOMONOCYTIC LEUKEMIA: SIMILARITIES AND DIFFERENCES MYELODYSPLASTIC SYNDROMES

Abstract

Background:Recently, 3 types of monocytes have been characterized by immunophenotyping in chronic myelomonocytic leukemia (CMML). Increase in monocytes in bone marrow (BM) may also be found in myelodysplastic syndromes (MDS). In a previous study using multiparameter flow cytometry to study BM myeloid precursors in MDS we found monocyte increase in 21% of the patients, with similar frequencies in RAEB and low risk MDS, but this was associated with a worse overall survival.Aims:to study the phenotypic characteristics of BM myelomonocytic precursors and CD34+ progenitors in CMML and compare them with findings observed in MDS.Methodswe studied cases of CMML and low risk MDS entering our Laboratory in 2018. Bone marrow (BM) was collected at the diagnostic work‐up. Diagnosis and classification of the cases was made by WHO 2016 criteria based on peripheral blood counts, BM morphology and cytogenetics. Cases of transitory peripheral cytopenias presenting normal results were used as controls. Immunophenotyping of BM cells was made with and 8‐color platform according to Euroflow. A minimum 300000 cells were acquired.Results:We examined 24 cases of MDS (age 27‐88 years), and 19 CMMLs (age 55‐90 years) which were compared with 12 controls (age 25‐79 years). Concerning immunophenotypic features, SSC of granulocytic precursors/SSC of lymphocytes <6 was seen in 10 MDS and in 9 LMMC cases. Abnormal antigen expression in granulocytic precursors was observed in 11/23 MDS (0 alterations = 12, 1 = 5 and 2 = 6) and 11/17 CMML (0 alterations = 7, 1 = 7 and 2 = 5). Total monocytes were increased in all CMMLs but also in 15 cases of MDS, with similar proportions of classical monocytes (median 94.7% and 93.1% respectively), but increase in monocytes in CMML was mostly dependent on increase in classical monocytes, while in MDS both classical and non‐classical forms increased. Myeloid CD34+ progenitors were >2% in 4 cases of CMML but in none of the MDS cases. Total lymphocytes increased in MDS, but decreased in CMML. In these later, the decrease was more prominent in mature B‐cells, but occurred also in T CD4+ cells.Summary/Conclusion:Immunophenotyping of BM in CMML discloses several abnormalities of monocytic but also of granulocytic precursors, similar to MDS. Besides, decrease in lymphoid cells is similar to what has been described in juvenile myelomonocytic leukemia but different from those seen in low risk MDS.