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Juvenile Myelomonocytic Leukemia (JMML)

What is Juvenile Myelomonocytic Leukemia?

Juvenile myelomonocytic leukemia (JMML) is a rare cancer of the blood and bone marrow.

JMML occurs most often in children younger than 4 years. About 10% of all cases develop in infants younger than 3 months.

Each year 1-2 children out of 1 million are diagnosed with JMML in the United States. That is 25-50 new cases a year.

JMML occurs when too many blood stem cells in the bone marrow become white blood cells called monocytes and myelocytes. They build up in the liver, spleen, bone marrow, and blood. The body can’t fight infection as well. The blood doesn’t function correctly.

JMML can be aggressive. Hematopoietic cell transplant is the most common treatment. But in 15% of cases, JMML will go away on its own without treatment. Doctors will closely monitor these cases.

The World Health Organization (WHO) classifies JMML among the myelodysplastic/myeloproliferative diseases because it has features of both types of diseases. JMML also shares some of the features of chronic myelomonocytic leukemia in adults.

Causes and Risk Factors of Juvenile Myelomonocytic Leukemia

Boys are twice as likely to be diagnosed as girls.

About 90% of patients have changes in certain genes that cause this cancer to develop. These changes are called mutations:

  • A gene mutation can either be inherited from a parent or it can occur in the body some time during the person’s life.
  • An inherited mutation is called a germline mutation.
  • Other mutations are called somatic or acquired mutations.
  • Knowing the specific genetic mutation and whether it is inherited or acquired later is important. This information helps determine treatment approaches.
  • But just because someone has a genetic mutation or condition does not mean he or she will develop cancer.

Signs and Symptoms of Juvenile Myelomonocytic Leukemia

Signs and symptoms of JMML are often similar to other childhood leukemias and blood disorders.

Many children will have:

  • Fever
  • Signs and symptoms of an upper respiratory infection, such as bronchitis or tonsillitis
  • Enlarged spleen
  • Painless swelling of lymph nodes
  • Skin rash

Other signs and symptoms of JMML may include:

Diagnosis of Juvenile Myelomonocytic Leukemia

Diagnosis of JMML is sometimes challenging. JMML has similar symptoms to viral or bacterial infections and other childhood leukemias and blood disorders.

Chromosomal and genetic testing is important because the type of mutation can help determine treatment.

Tests to diagnose JMML include:

  • Physical exam and history
  • Blood tests (complete blood count and blood chemistry)
  • Bone marrow tests
  • Tests to examine chromosome and gene changes
  • Genetic testing (skin or hair follicles) to help determine if mutations are inherited or acquired (occurring after birth).

Treatment for Juvenile Myelomonocytic Leukemia

Treatment ranges from watchful observation to hematopoietic cell transplantation.

Doctors prescribe treatment based on how well patients are predicted to respond. This approach is called risk-adapted or risk-stratified.

The course of the disease and treatment response varies widely. Doctors may use age, level of fetal hemoglobin, and platelet count in part to help predict these things. Most children require transplant. In about 15% of cases, the disease will eventually resolve on its own without treatment.

At present, hematopoietic cell transplant (also known as bone marrow transplant or stem cell transplant) is the only treatment that can provide cure. Patients must have a suitable donor to get this treatment.

The transplant should occur as soon as possible after diagnosis because successful transplant rates are highest in younger children. If the JMML relapses, a second hematopoietic cell and natural killer cell transplant have shown success.

Umbilical cord blood transplants are also a treatment option.

Other treatments may include:

  • Chemotherapy
  • Targeted therapy drugs
  • Surgical removal of the spleen if it has become severely enlarged

Treatment of children with inherited syndromes may be different that of children who acquired the mutation.

Prognosis of Juvenile Myelomonocytic Leukemia Treatment

  • A hematopoietic cell transplant may successfully treat more than 50% of cases.
  • In about 35% to 40% of children who achieve remission with a transplant, the JMML comes back within the first year. Doctors may recommend a second transplant.

Focus of Current JMML Research

Developing targeted therapies is a current focus of research. Scientists are studying new ways to create renewable sources of cells for research on JMML. This may help in researching potential new targeted therapy approaches.

Researchers are developing better ways to predict the course of disease. These include study of a cellular process called DNA methylation. Diseases such as cancer may develop when DNA methylation is abnormal.

Researchers are looking for ways to reduce the rate of relapse that occurs in 35% of cases. One approach under study is an oral MEK inhibitor drug called trametinib in relapsed JMML.


Reviewed: December 2019