Juvenile myelomonocytic leukemia
A rare childhood leukemia with distinct diagnostic criteria and treatment protocols.
Juvenile myelomonocytic leukemia (JMML) is a rare chronic leukemia that primarily affects children aged four and younger, with an average diagnosis age of two years. It is classified as a subcategory of myelodysplastic and myeloproliferative disorders by the World Health Organization. The term JMML now encompasses what were previously called juvenile chronic myeloid leukemia, chronic myelomonocytic leukemia of infancy, and infantile monosomy 7 syndrome.
Quick Facts
- Onset
- Under 3 years old
- Treatment
- Stem cell transplant
- Frequency
- One to two children out of one million diagnosed each year
Facts from the source article.
Diagnosis
Diagnosis requires all four of the following: absence of the Philadelphia chromosome or BCR/ABL fusion gene, peripheral blood monocytosis greater than 1 billion per liter, less than 20% blasts (including promonocytes) in blood and bone marrow, and splenomegaly. Additionally, at least one of these must be present: a mutation in RAS or PTPN11, a diagnosis of neurofibromatosis 1, or chromosome 7 monosomy. Alternatively, two or more of several other criteria, such as elevated hemoglobin F for age or white blood cell count over 10 billion per liter, may suffice. Infectious diseases like Epstein–Barr virus and cytomegalovirus are considered in the differential diagnosis.
Treatment
Two widely used treatment protocols exist: stem cell transplantation and drug therapy. Internationally accepted protocols differ by region, with the Children's Oncology Group study used in North America and the European Working Group for Myelodysplastic Syndromes study used in Europe. Patients scheduled for splenectomy are advised to receive vaccines against Streptococcus pneumoniae and Haemophilus influenza at least two weeks prior, and daily penicillin may be required afterward indefinitely. The role of chemotherapy before bone marrow transplant remains unconfirmed, and chemotherapy alone does not produce long-term survival. Low-dose conventional chemotherapy has not been shown to influence survival length, though some combinations of 6-mercaptopurine with other drugs may reduce organ size and improve blood counts.
Prognosis
Without treatment, survival for children under five is approximately 5%. Only hematopoietic stem cell transplantation (HSCT) can cure JMML, with recent studies reporting a survival rate of about 50% after transplant. Relapse is the leading cause of death in transplanted children, with a relapse rate as high as 50%, often occurring within months after transplant; the risk drops considerably after one year. Many children who relapse achieve complete remission and long-term cure after a second stem cell transplant, so this option should always be considered.
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