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About Juvenile Myelomonocytic Leukemia (JMML)

  • Juvenile myelomonocytic leukemia (JMML) is a rare type of blood cancer that occurs when bone marrow production of white blood cells becomes severely dysregulated. In children with JMML, bone marrow — the soft, spongy center of the bones responsible for creating blood cells — produces immature white blood cells that grow too rapidly and keep reproducing even when they run out of space. This crowds out healthy bone marrow cells and can lead to symptoms such as infections, anemia, and bleeding. Currently, the only cure for JMML is stem cell transplant.

    Children and teens with JMML are treated at Dana-Farber/Boston Children's Cancer and Blood Disorders Center through the Childhood Leukemia Program, one of the top programs worldwide for pediatric leukemia. Our program has been instrumental in refining treatments for childhood leukemia, which has resulted in improved cure rates and decreased side effects. We also have one of the largest and most experienced pediatric stem cell transplant programs in the U.S.

    Dana-Farber/Boston Children's offers a wide array of support services and programs for pediatric patients and their families during and after cancer treatment.

    Symptoms of Juvenile Myelomonocytic Leukemia (JMML)

    Because JMML is a cancer of the blood-forming bone marrow, initial symptoms are often related to abnormal bone marrow function. The bone marrow is responsible for storing and producing about 95 percent of the body's blood cells, including the red blood cells, white blood cells, and platelets. While each child may experience symptoms of JMML differently, some of the most common symptoms include:

    • General fatigue or weakness
    • Recurrent infections: Although there may be an unusually high number of white blood cells on your child's blood count, these white blood cells are immature and do not fight infection. Your child may have had several viral or bacterial infections over the course of a few weeks and may show symptoms of an infection such as fever, runny nose, and cough.
    • Bone and joint pain: Your child may experience pain in his bones and joints. This pain is usually a result of the bone marrow being overcrowded and "full."
    • Abdominal pain: Stomach aches may also be a symptom of JMML. Leukemia cells can collect in your child's kidney, liver, and spleen, causing enlargement of these organs. Pain in the abdomen may cause your child to lose his appetite and lose weight.
    • Swollen lymph nodes: Your child may have swelling in the lymph nodes under the arms, in the groin, in the chest, and in the neck. Leukemia cells may collect in the nodes, causing this swelling.

    Symptoms of JMML may resemble other blood disorders or medical problems. Because many of these symptoms can also point to other conditions, it's important to have your child evaluated by a qualified medical professional right away for an accurate diagnosis and prompt treatment.

    Causes of Juvenile Myelomonocytic Leukemia (JMML)

    About 90% of children diagnosed with JMML have been found to have specific genetic mutations. These mutations occur in a type of white blood cell known as a monocyte, which are a part of the body's immune system. Children with Neurofibromatosis type 1 and Noonan syndrome are more likely to develop JMML.

    It's important to understand that there's nothing you could have done or avoided doing that would have prevented your child's cancer from developing.