This new WHO group includes the following disorders: atypical (true ph' chromosome/BCR-ABL negative CML)
chronic myeloid leukemia (a-CML), Juvenile myelomonocytic leukemia (JMML), and chronic myelomonocytic
leukemia (CMML). These disorders have features of both myeloproliferative and myelodysplastic syndromes.
The bone marrow biopsy findings include the presence of an increased number of blasts which can be
highlighted by using CD34 immunostaining. In cases of JMML and CMML the marrow may also contain an
increased number of monocytic cells reactive with CD68. The differential diagnosis of JMML is based on a
multiparametric approach which includes among other the assessment of HBF and karyotype. In the work up of
JMML, bone marrow biopsy can be very useful in narrowing down the differential diagnosis, e.g. by excluding
an infection associated hemophagocytic syndrome in patients with low WBC counts and organomegaly or in
ruling out acute leukemia. The blast cell in JMML are poorly differentiated myelomocytic. They express
CD34 and are only rarely positive with myeloperoxidase. A proportion of the cells express CD68 (PG-M1) and
lysozyme. The presence of numerous S-100 positive histiocytes has been reported in a few JMML cases (Ng et
- Harris et al: The World Health Organization classification of hematological malignancies report of the
Clinical Advisory Committee Meeting, Airlie House, Virginia, November 1997. Mod Pathol. 2000
- Hess et al: Juvenile chronic myelogenous leukemia (review). Am J Clin Pathol 1996; 105:238-248.
- Ng et al: Juvenile chronic myeloid leukemia. A malignancy of S-100 protein-positive histiocytes. Am J
Clin Pathol. 1988 Nov;90(5):575-82.