Chronic Myelomonocytic Leukemia (CMML)
Definition
- Malignant neoplasm exhibiting both myelodysplastic and myeloproliferative features and characterized by peripheral monocytosis
Diagnostic Criteria
- Diagnosis requires ALL of the following five criteria
- Persistent blood monocytosis, >1 x
103/μL AND
- Usually mature but may have abnormal granules or nuclei (abnormal monocytes)
- Neutrophilia and/or eosinophilia (see below) may be present
- No Philadelphia chromosome or BCR-ABL1 fusion AND
- No abnormalities of PDGFRA or PDGFRB or 11q23 (which suggest AML) AND
- Blasts plus promonocytes <20% in both bone marrow and peripheral blood
AND
- If ≥20%, diagnose as AML
- Any one of the below features:
- Dysplasia in one or more myeloid lineages (most common)
- Demonstration of an aquired clonal cytogenetic or molecular genetic abnormality in the marrow
- At least 3 months duration of monocytosis, with other causes ruled out (see Differential Diagnosis)
- Persistent blood monocytosis, >1 x
103/μL AND
- Systemic mastocytosis may coexist with CMML
- (WHO category SM-AHNMD)
- CMML should be divided into prognostic groups:
- CMML-1
- Blasts + promonocytes <5% in blood and <10% in marrow
- CMML-2
- Blasts + promonocytes 5-19% in blood and 10-19% in marrow OR
- Auer rods present in blood or marrow
- CMML-1
- CMML with eosinophilia may be diagnosed if blood eosinophils >1.5 x 103/μL
- All other CMML criteria must be fulfilled, including lack of PDGFRA and PDGFRB abnormalities
- May exhibit tissue damage from eosinophilia (see Clinical)
- Bone marrow is usually hypercellular with dysplastic features
- Occasional cases may be hypocellular
- Nodules of plasmacytoid dendritic cells present in 20% of cases
- Monomorphous cells with sharp borders and round nuclei
- Inconspicuous nucleoli, fine chromatin
- CD123 positive
- Reticulin stain may show mild to moderate fibrosis
- Spleen frequently shows red pulp involvement
- Any of the following
may be found in extramedullary sites such as skin and lymph nodes
- CMML
- Plasmacytoid dendritic cell nodules
- Blastic transformation
Dita Gratzinger MD PhD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342
Original posting: 11/6/11
