Discussion

Chronic Myelomonocytic Leukemia (CMML) is a malignant condition of the blood and bone marrow. Diagnostic criteria for CMML are absolute monocytosis greater than 1 x 109/L in peripheral blood, increased bone marrow monocytes and dysplasia in all three-cell lineages. There can be extramedullary leukaemic infiltration of the spleen, liver, skin and lymph nodes. 

Microscopically the monocytes will be mature with unusual nuclear lobulation, abnormal granulation and finely dispersed chromatin. The blasts have to be less than 20% or the correct diagnoses become AML.

The immunophenotype will have myelomonocytic antigens, CD33, CD13 and CD15. There may be variable expression of the monocytic antigens, CD14, CD68 and CD64. The blasts may also express CD 34.

Genetically the most important thing is CMML does not show a Philadelphia chromosome. Although 20-40% demonstrate cytogenetic abnormalities with+8,-7/del (7q) and structural abnormalities of 12p being the most common, there is no one specific chromosomal abnormality as in CML. There are two controversies with this diagnosis. The first controversy involves classification of CMML. Is CMML a MPS or and MDS.

The French-American-British (FAB) group divides this leukemia into the two groups based on the white blood cell (WBC) counts. If there is leukocytosis of greater than or equal to 13,000 x 109/L, CMML is classified as MPS but if the WBC count is < 13,000 x 109/L CMML is classified as MDS. The second controversy exists with some authors believing that CMML, Juvenile Myelomonocytic Leukemia (JMML) and CML are variations of the same disease process. The World Health Organization Classification of Tumors of Haematopoietic and Lymphoid Tissues states there is sufficient clinical, morphologic and biological differences for separate classification of each of these entities.

The bone marrow in CMML patients can progress to type of acute leukemia, either myeloid or monocytic or a combination of myeloid and monocytic. CMML generally does not completely respond to chemotherapy. Allogenic bone marrow transplant can be curative, but it is less successful than in CML. The extended prognosis for some CMML patients is transformation to acute leukemia. Others will require red cell and platelet transfusions as well as have problems with infection. The median survival is 20 to 40 months and 39% at 3 years for patients’ status post allogenic bone marrow transplantation 

References 

1. Hess JL. Chronic Myelomonocytic Leukemia (CMML). Atlas Genet Cytogenet Oncol Haematol. July 2001

2. URL : http://www.infobiogen.fr/services/chromcancer/Anomalies/CMMLID1098.html

3. Jaffe E.S., Harris N.L., Stein H., Vardiman J.W. (Eds.): World Health Organization Classification of Tumors. Pathology and Genetics of Tumours of Haematopoietic and Lymphoid Tissues. IARC Press: Lyon 2001

4. Onida F, Kantarjian HM, Smith TL, et al. Prognostic factors and scoring system in chronic myelomonocytic leukemia: a retrospective analysis of 213 patients.  Blood 99:840-9, 2001