Chronic myelomonocytic leukemia (CMML) is classified by the WHO as a mixed myelodysplasia and myeloproliferative disorder. It can be defined based on hematologic and cytologic findings.
General features:
(1) persistent monocytosis > 1,000 per µL in the peripheral blood
(2) < 20% blasts in blood or bone marrow
(3) one of the following:
(3a) dysplasia in one or more marrow cell lines
(3b) the monocytosis has lasted for at least 3 months and all other causes of monocytosis have been excluded
(3c) there is an acquired, clonal cytogenetic abnormality in the bone marrow
where:
• Blasts include myeloblasts, monoblasts and promonocytes.
Exclusions:
(1) Philadelphia chromosome
(2) BCR/ABL fusion genes
(3) >= 20% blasts in blood or bone marrow (indicates AML)
Subtypes of CMML:
(1) CMML-1
(2) CMML-2
(3) CMML with eosinophilia
Subtype
Features
CMML-1
< 5% blasts in the peripheral blood AND < 10% blasts in the bone marrow AND no Auer rods
CMML-2
(a) 5-19% blasts in the peripheral blood, or (b) 10-19% blasts in the bone marrow or (c) Auer rods present with blast count < 20% in bone marrow or peripheral blood
CMML-1 or CMML-2 with eosinophilia
as above, with absolute eosinophil count > 1,500 per µL
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