Juvenile myelomonocytic leukemia (JMML)

What is juvenile myelomonocytic leukemia (JMML)

Juvenile myelomonocytic leukemia (JMML) is an uncommon blood cancer that most often occurs in infants and toddlers. It is similar in some ways to adult chronic myelomonocytic leukemia (CMML); in both JMML and CMML, mutations (changes) in the DNA take place in an early progenitor cell, which leads to increased numbers of white blood cells called “monocytes.”  

JMML has overlapping features of two other types of blood cancers: myelodysplastic syndromes (MDS) and myeloproliferative neoplasms (MPNs). The World Health Organization (WHO) has classified JMML as “myelodysplastic/myeloproliferative neoplasms.” 

Over time, JMML has been known by other names, such as “juvenile chronic myeloid leukemia,” “CMML of childhood,” “chronic and subacute myelomonocytic leukemia,” and “infantile monosomy 7 syndrome.”

JMML accounts for approximately 1 percent to 2 percent of all childhood leukemia cases. It has an incidence of 1.2 cases per million children per year. The median age at diagnosis is 2 years. The disease occurs most commonly in infants and children younger than 4 years but can present in older children, particularly those with neurofibromatosis type 1.  

Patients should be treated by a pediatric hematologist-oncologist, a specialist who treats children with JMML or other types of blood cancer.  

Download a copy of Caring for Kids and Adolescents with Blood Cancer: A Workbook for Families which provides information, resources, and worksheets to use throughout your child's cancer journey. You can also call an Information Specialist at 800.955.4572 to order a physical copy.  

What should I do if my child is diagnosed with JMML?

• Talk with your doctor about your child's diagnostic tests and what the results mean.
• Seek treatment in a cancer center where doctors are experienced in treating patients with leukemia.
• Ask your doctor whether a clinical trial is a good treatment option for your child. 

Learn more about communicating with your blood cancer specialist or find a list of suggested questions to ask your healthcare providers.  

After diagnosis: Navigating your child's care 

Navigating your child’s blood cancer care isn’t always simple or straightforward—but we’re here to guide you through it. Whether they’re newly diagnosed or in remission, you’ll find the information, support, and resources you need to navigate every step of your child’s blood cancer journey. 

Visit Navigating your care: Children and teens

How does JMML develop?

JMML starts in the bone marrow when stem cells acquire mutations that lead to the overproduction of monocytes (a type of white blood cells). These “myeloproliferating” cells accumulate in the marrow and in other organs including the spleen, the liver, and even the lungs and skin.

When the spleen becomes enlarged, sometimes dramatically so, there is less room in the abdomen and chest for other organs, causing discomfort. JMML cells can infiltrate the lungs and lead to breathing problems. As too many white blood cells are being produced, there is almost always decreased production of red blood cells and platelets, leading to decreased energy and increased risk of bleeding and bruising. 

What are risk factors for JMML?

Doctors don't know why some cells become JMML and others don't; however, scientists have established a link between JMML and a rare genetic condition called neurofibromatosis 1. 

Source: Chronic Myelomonocytic Leukemia (CMML) and Juvenile Myelomonocytic Leukemia (JMML). Reviewed by Mrinal Patnaik, MBBS, and Elliot Stieglitz, M.D.