Immunophenotype in Chronic Myelomonocytic Leukemia: Is It Closer to Myelodysplastic Syndromes or to Myeloproliferative Disorders?.

Chronic myelomonocytic leukaemia (CMML) is an entity with a heterogeneous clinical evolution, initially included among myelodysplastic syndromes (MDS) according to the FAB classification. The recent WHO classification brings CMML closer to myeloproliferative disorders, and moved it into a new category termed myelodysplastic/myeloproliferative diseases (MDS/MPD).

Aim: To describe the immunophenotypic profile of CMML and to compare it with the phenotype described in MDS and MPD. Patients: 76 patients: 20 CMML (15 CMML I, 5 CMML II), 38 MDS (refractory cytopenia with multilineage dysplasia), and 18 MPD (11 essential thrombocytemia, 2 chronic idiopathic myelofibrosis, and 5 polycythemia vera).

Material and Methods: Flow cytometry immunophenotyping (FCI) in bone marrow samples. Data studied: 1 In the myeloid lineage: abnormalities in granularity and CD45 distribution, abnormalities in the phenotypic pattern of myeloid development (CD16/CD11b/CD13), and the absence of CD10 expression on mature granulocytes (CD10−). 2 In the monocytic lineage: CD2 and CD56 expression. 3 In the red cells: abnormalities in CD71 and glycophorin A distribution. 4 In B-cells, detection of a low percentage of CD10+ B-cell precursors (less than 1% of bone marrow B-cells). 5 In myeloblasts, identification of more than >5% CD34+ cells, and evaluation of aberrant expression of CD7 and TdT in these cells (positive expression was described when >10% of CD34+ cells were positive for any of these antigens).

Results: Abnormal cases among those studied for each parameter analysed is specified in the table. Patients with CMML and MDS showed statistically significant differences (p<0.05) in their B-cell development and CD56 monocyte expression. Significant differences between CMML and MPD were found in CD45 myeloid distribution, myeloid antigenic profile, CD56 and CD2 monocyte expression and B-cell development.

Conclusions: With the number of cases studied, higher similarities can be found between CMML and MDS immunophenotypic profiles. The antibody panel selected, including several abnormalities previously described in patients with MDS, might justify the differences found between CMML and MPD. However, it does not explain the relationship between the immunophenotypic profile of CMML and MDS. Abnormalities in B-cell development and aberrant expression of CD56 on monocytes were the most useful data to distinguish CMML and MPD. Although the number of patients studied is still low, quantification of CD34+ cells did not help to identify CMML with an aggressive clinical course.