Juvenile Myelomonocytic Leukemia (JMML) is a cancer of the white blood cells. It is characterized by overproduction of myelocytes and monocytes; this chronic proliferation of myelocytes and monocytes in the bone marrow prevents the formation of healthy red blood cells, white blood cells, and/or platelets. Since JMML is characterized both by dysregulation and excessive proliferation of the bone marrow, it is classified as a mixed myelodysplastic-myeloproliferative disorder. The pathologic features of JMML are believed to primarily be the result of a clonal abnormality leading to activation of Ras signaling; this inappropriate activation of Ras leads to over-proliferation of certain cell types. Approximately 75% of all JMML patients carry one of three mutually exclusive mutations associated with inappropriate Ras activation: direct RAS mutations; NF1 -inactivating mutations; or protein tyrosine phosphatase, non-receptor type 11 (PTPN11) mutations.1

Clinically, JMML presents as hepatosplenomegaly with or without lymphadenopathy, pallor, fever, and rash. Due to the broad differential diagnosis associated with this presentation, a diagnosis of JMML may require a very extensive workup. JMML most commonly affects children less than six years of age, with most patients diagnosed at less than two years of age. It comprises less than 2% of all childhood leukemias, and has historically carried a grim prognosis, with less than 10% survival with a chemotherapy-only approach.1 With HCT, survival approaches 50%.2

1 National Cancer Institute. Childhood Acute Myeloid Leukemia/Other Myeloid Malignancies Treatment (PDQ®), Health Professionals handout. Accessed at: http://www.cancer.gov/cancertopics/pdq/treatment/childAML/HealthProfessional
Accessibility verified August 8, 2013.

2 Locatelli F, Nollke P, Zecca M, et al. Hematopoietic stem cell transplantation (HSCT) in children with juvenile myelomonocytic leukemia (JMML): results of the EWOG-MDS/EBMT trial. Blood. 2004;105(1):410-419.

JMML Response Criteria
2015: JMML Pre-HCT
2115: JMML Post-HCT

Last modified: Feb 27, 2015

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