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Juvenile Myelomonocytic Leukemia

What is juvenile myelomonocytic leukemia?

Juvenile myelomonocytic leukemia (JMML) is a rare and serious form of childhood leukemia (blood cancer).

Blood stem cells are made in the bone marrow. JMML occurs when too many blood stem cells become white blood cells called monocytes and myelocytes. Some of the monocytes and myelocytes mature into normal white blood cells, but many of them never fully mature. These immature white blood cells are called blasts.

Over time, the myelocytes, monocytes and blasts crowd out the healthy red blood cells and platelets in the bone marrow. This may cause infection, anemia or bleeding problems. JMML can also spread from the bone marrow to other areas of the body such as the skin, lungs, liver or intestines.

How common is juvenile myelomonocytic leukemia?

JMML occurs most often in children younger than 4 years. Ten percent of all cases develop in infants younger than 3 months. One to two children out of a million are found to have JMML each year. The disease accounts for 1.6% of all blood-related cancers. Boys are twice as likely to get JMML as girls.

Children who have neurofibromatosis type 1 [EJW1] (NF1) have an increased risk of developing JMML. NF1 is a genetic condition that causes the following:

  • brown spots and tumors on the skin
  • freckles on skin not exposed to the sun
  • tumors on the nerves
  • developmental changes in the nervous system, muscles, bone and skin

What are the signs and symptoms of juvenile myelomonocytic leukemia?

Some of the more common symptoms of JMML include the following:

  • Fever for no known reason
  • Infections, such as bronchitis or tonsillitis
  • Feeling very tired
  • Easy bruising or bleeding of the skin, nose and mouth
  • Red skin rash or tiny, red pinpoint dots on the skin
  • Painless swelling of the lymph nodes in the neck, underarm, stomach or groin
  • Pain or a feeling of fullness below the ribs
  • Dry cough
  • Trouble gaining weight
  • Poor appetite
  • Failure to thrive
  • Feeling irritable
  • Enlarged spleen or liver
  • Anemia

How is juvenile myelomonocytic leukemia treated?

At present, the only treatment for JMML that offers hope of a long-term cure is stem cell transplantation. This transplant uses healthy bone marrow stem cells or umbilical cord stem cells donated by another person. This kind of transplant is called an allogeneic stem cell transplant.

A patient’s brother or sister is usually the best match to donate stem cells for transplantation. If a sibling is not available, one of the patient’s parents or someone outside of the patient’s family can be a suitable donor. The stem cell transplant should be done as soon as possible after diagnosis, because successful transplant rates are highest in younger children.

What are the survival rates for juvenile myelomonocytic leukemia?

For children with JMML who do not receive treatment only about 5% to 10% will get better. With allogeneic stem cell transplant, many children with JMML are cured of their cancer.

In about 35% to 40% of children who achieve remission (no sign of cancer) with an allogeneic stem cell transplant, the JMML comes back within the first year. A second stem cell transplant has been shown to be effective for these patients.

Why choose St. Jude for your child’s juvenile myelomonocytic leukemia treatment?

  • St. Jude is the only National Cancer Institute-designated Comprehensive Cancer Center devoted solely to children.
  • St. Jude has created more clinical trials for cancer than any other children’s hospital in the United States.
  • The nurse-to-patient ratio at St. Jude is unmatched— averaging 1:3 in hematology and oncology, and 1:1 in the Intensive Care Unit.
  • Successful treatment for JMML requires a stem cell transplant. St. Jude has one of the world’s largest bone marrow/stem cell transplant programs dedicated to children, teens and young adults. Since the first hematopoietic stem cell transplant at St. Jude was performed in 1982, the Transplant Program has performed more than 2,900 transplants.
  • St. Jude is accredited by the Foundation for the Accreditation of Cellular Therapy (FACT) for autologous and allogeneic peripheral blood and marrow transplantation in children and adults.
  • The Transplant Program at St. Jude has been a part of the National Marrow Donor Program (NMDP) since 1990. Our center also provides data to the International Bone Marrow Transplant Registry and the Autologous Bone Marrow Transplant Registry.
  • To improve outcomes and reduce side effects associated with transplants, doctors in the St. Jude Transplant Program work closely with laboratory scientists to rapidly move discoveries from the lab to the clinic.
  • St. Jude support staff members have been specially trained to care for children receiving stem cell transplants.

Associated Clinical Trials


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