An Overview of Juvenile Myelomonocytic Leukemia

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Juvenile myelomonocytic leukemia (JMML) is a rare and aggressive blood cancer that affects infants and young children. JMML accounts for less than 1% of childhood leukemias and is generally diagnosed by the age of two. It is more than twice as common in boys as it is in girls.

A young boy with cancer playing with geese / Maksi Mages

JMML is also referred to as juvenile chronic myelogenous leukemia (JCML), juvenile chronic granulocytic leukemia, chronic and subacute myelomonocytic leukemia, and infantile monosomy 7.


The signs and symptoms of JMML are related to the accumulation of abnormal cells in the bone marrow and organs. They may include:

  • Pale skin
  • Recurrent fevers or infection
  • Abnormal bleeding or bruising
  • Swollen abdomen due to an enlarged spleen or liver
  • Swollen lymph nodes
  • Rash
  • Decreased appetite
  • Chronic cough
  • Difficulty breathing
  • Developmental delays
  • Bone and joint pain

These can also be signs and symptoms of other noncancerous conditions. If you are concerned about your child's health, the best thing to do is to visit your healthcare provider.

Disease Progression

The course of JMML can vary from one child to the next. Broadly speaking, there are three distinct ways that JMML acts:

  • In the first type, the disease progresses rapidly.
  • In the second type, there is a transient period when the child is stable, followed by a rapidly progressive course.
  • In the third type, children may improve and remain only mildly symptomatic for up to nine years, at which time the disease becomes rapidly progressive unless appropriately treated.


JMML occurs when genetic mutations develop in the DNA of bone marrow. This will cause the bone marrow to produce misshapen white blood cells (namely monocytes) that fail to mature and begin to rapidly multiply out of control.

As the numbers of abnormal cells increase, they will begin to take over the bone marrow and interfere with its primary main job, which is to produce healthy red blood cells, white blood cells, and platelets.

Scientists have yet to identify the specific combinations of mutations needed to trigger JMML but have found that mutations of the NF1, NRAS, KRAS, PTPN11, and CBL genes occur in 85% of children with JMML. All of these mutations can be inherited from parents.

Children with neurofibromatosis type I and Noonan syndrome have an increased risk of JMML. In fact, up to 20.8% of children diagnosed with JMML will also have Noonan syndrome (a rare genetic disorder that prevents normal development in various parts of the body).


To diagnose JMML, doctors will examine the results of blood tests as well as bone marrow aspiration and biopsy. These samples can undergo genetic testing to identify the mutations strongly associated with JMML. Certain findings are strongly indicative of JMML:

  • An elevated white blood cell count (especially high monocytes)
  • Low red blood cell count (anemia)
  • Low platelet count (thrombocytopenia)
  • Abnormalities in chromosome 7

Imaging tests (such as an X-ray, CT scan, MRI, or ultrasound) may be used to check for a mass of leukemia cells in the chest that could affect breathing or blood circulation.

The lack of the Philadelphia chromosome will help differentiate JMML from a similar condition called chronic myelogenous leukemia (CML).


Unlike other forms of cancer, JMML tends to have a poor response to chemotherapy. Purinethol (6- mercaptopurine) and Sotret (isotretinoin) are drugs that have been used with a small measure of success. Because of its limited benefit in the treatment of JMML, chemotherapy is not the standard.

Allogeneic stem cell transplant is the only treatment that can offer a long-term cure for JMML. Similar rates of success are seen with matched family stem cell donors or matched non-family donors.

Research suggests that the rate of JMML relapse after a stem cell transplant may be as high as 50%. Relapse almost always occurs within a year. Despite the discouraging numbers, children with JMML often achieve sustained remission after a second stem cell transplant.

The role of surgery in the treatment of JMML is controversial. One protocol issued by the Children’s Oncology Group (COG) recommends the removal of the spleen (splenectomy) in children with JMML who have an enlarged spleen. It is unknown if the long-term benefit of the surgery outweighs the risks.

Despite the need for aggressive treatment, children with JMML are doing much better than ever before. One study reported that the five-year survival rate for children who undergo a stem cell transplant is between 50% and 55%.

Progress is being made every day to improve upon these figures.

A Word From Verywell

As a parent, one of the most difficult things to imagine is your baby or child getting sick. This type of illness can put a tremendous strain on the child and the rest of the family. You may be struggling to explain a complicated situation to your children, without being able to wrap your head around it yourself.

Take advantage of any support groups or resources offered by your cancer center as well as support from loved ones, friends, family, and neighbors. While you and your family may be experiencing a wide range of emotions and feelings, it is important to remember that there is hope for a cure and that some children with JMML go on to lead healthy and productive lives.

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7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Karen Raymaakers
Karen Raymaakers RN, CON(C) is a certified oncology nurse that has worked with leukemia and lymphoma patients for over a decade.