Bone marrow biopsy in chronic myelomonocytic leukaemia, CMML

Definition

CMML has features intermediate between a myeloproliferative and a myelodysplastic syndrome. The WHO definition requires more than 1 x 109 monocytes / litre in the peripheral blood and more than 10% of white cells to be monocytes.

CMML type 1 has less than 5% blasts in the blood or less than 10% blasts in the bone marrow
CMML type 2 has 5-19% blasts in the blood or 10-19% blasts in the bone marrow
AML has more than 20% blasts and promyelocytes in the bone marrow
Chronic myelogenous leukaemia (CML) and atypical chronic myeloid leukaemia (aCML) also show myeloid proliferation

Histopathology

The bone marrow is hypercellular with significant granulocytic proliferation. Erythroid precursors and megakaryocytes may be normal or dysplastic. Monocytic proliferation is difficult to detect morphologically but can be demonstrated by butyrate esterase staining.

Immunohistochemistry

	CMML-1	CMML-2	CMML in acute transformation	CML	atypical CML
CD34	3.1%	12%	39%	3.8%	3.6%
CD68, KP1	27%	56%	23%	91%	72%
CD68R, PG-M1	4.3%	2.6%	2.8%	2.8%	1%
CD163	2.5%	4.4%	4.1%	2.0%	1.0%
CD123	4/20	2/5	1/7	0/6	0/3

PG-M1 and CD163 both fail to clearly differentiate between CMML and CML. CD123 appears to have a useful ability to visualise nodular proliferations of plasmacytoid monocytes in CMML. CD34 is useful in demonstrating the excess blasts seen in CMML in acute transformation.

Differential diagnosis

CML
atypical CML

References

1 Orazi A, Chiu R, O'Malley DP, et al. Chronic myelomonocytic leukemia: The role of bone marrow biopsy immunohistology. Mod Pathol 2006; 19:1536-45

This page last revised 3.1.2007.