What Is Juvenile Myelomonocytic Leukemia? Juvenile myelomonocytic leukemia (JMML) is a rare childhood cancer. It happens when immature blood cells (called blasts) make too many myelocytes and monocytes (two types of white blood cells). These myelocytes, monocytes, and blasts crowd the normal cells in the bone marrow and other organs in the body, causing the symptoms of JMML. Who Gets Juvenile Myelomonocytic Leukemia? Juvenile myelomonocytic (mye-eh-low-mah-nuh-SIT-ik) leukemia usually happens in children younger than 4 years old. What Are the Signs & Symptoms of Juvenile Myelomonocytic Leukemia? JMML develops over time. A child may have very few symptoms at first because they can take months to develop. A child with juvenile myelomonocytic leukemia might: develop anemia, which is when the bone marrow doesn't make enough red blood cells get infections often (such as or tonsillitis) because the white blood cells don't fight germs as usual feel tired and weak because of anemia and infections have swollen lymph nodes from collected cancer cells have fevers from infections have easy bruising or bleeding because the bone marrow doesn't make enough platelets (cells that help clotting) have bone and joint pain because the bone marrow is full of abnormal cells have belly pain and swelling if abnormal blood cells build up in organs like the kidneys, liver, and spleen What Causes Juvenile Myelomonocytic Leukemia? Many children diagnosed with juvenile myelomonocytic leukemia have a change in their genes (a mutation). The change happens in monocytes (MAH-nuh-sites), which are part of the immune system. Some medical conditions — such as neurofibromatosis type 1 and Noonan syndrome — can make a child more likely to develop JMML. How Is Juvenile Myelomonocytic Leukemia Diagnosed? Doctors use special tests when they suspect leukemia. These include: Blood tests. Tests such as a complete blood count, liver and kidney function panels, and blood chemistries can give important information about the number of normal blood cells and how well the organs are working. The shapes and sizes of the blood cells are checked with a microscope. Imaging studies. These may include an X-ray, CT scan, MRI, or ultrasound. These can see whether there's a mass of leukemia cells in the chest that could affect breathing or blood circulation. They also can rule out other possible causes of a child's symptoms. Bone marrow aspiration and biopsy. The doctor puts a needle into a large bone, usually the hip, and removes a small amount of bone marrow. Then the lab does these tests on the bone marrow sample: Flow cytometry tests. Doctors look at the cancer cells and figure out the type of leukemia. This is important because treatment differs depending on the type. Genetic tests. By looking at the blood or bone marrow, doctors check for changes in the genes. The changes can help doctors figure out the best treatment. Spinal tap (lumbar puncture). The doctor uses a small hollow needle to remove a tiny amount of cerebrospinal fluid (the fluid surrounding the brain and spinal cord) for exam in a lab. Tissue typing or HLA (human leukocyte antigen) typing. If a child needs a stem cell transplant (bone marrow transplant), this test helps doctors find a suitable stem cell donor. It works by comparing the proteins on the surface of a child's blood cells with the proteins on a potential donor's cells. The more HLA markers a child and donor share, the greater the chances that a transplant will be successful. How Is Juvenile Myelomonocytic Leukemia Treated? Chemotherapy (the use of drugs to kill cancer cells) may be used to temporarily control juvenile myelomonocytic leukemia. But the most effective treatment is a stem cell (bone marrow) transplant. To do this, doctors: Give high-dose chemotherapy to destroy cancer cells and normal bone marrow and immune system cells. Put healthy donor stem cells into the body. The new stem cells can rebuild a healthy blood supply and immune system. Researchers are looking into the use of alternative treatments, such as: Molecular-targeted therapies: These medicines slow the growth of cancer cells by blocking certain molecules or proteins that help cancer cells grow. Immunotherapy: These medicines mark cancer cells so that the body's immune system can find them and remove them from the body. What Else Should I Know? Having a child being treated for cancer can be stressful for any family. But you're not alone. To find support, talk to your doctor or a hospital social worker. Many resources are available to help you get through this difficult time. You also can find information and support online at: NORD Juvenile Myelomonocytic Leukemia Foundation Back to Articles Related Articles Leukemia Leukemia refers to cancers of the white blood cells. With the proper treatment, the outlook for kids with leukemia is quite good. Read More Chronic Myelogenous Leukemia (CML) While this type of blood cancer is more common in adults, it affects children, too. Thanks to advances in therapy, most kids with CML can be cured. Read More Acute Lymphoblastic Leukemia (ALL) Acute lymphoblastic leukemia (ALL) is the most common type of childhood cancer. Because it develops and gets worse quickly, prompt treatment is very important. With treatment, most kids are cured. Read More Acute Myeloid Leukemia (AML) Acute myeloid leukemia (AML) happens when the body makes too many immature white blood cells. Among kids with leukemia, 20% have this type. With treatment, most recover. Read More Stem Cell Transplants Stem cells help rebuild a weakened immune system. Stem cell transplants are effective treatments for a wide range of diseases, including cancer. Read More Anemia Anemia happens when there aren't enough healthy red blood cells in the body. It can be caused by many things, including dietary problems, medical treatments, and inherited conditions. Read More Cancer Center From treatments and prevention to coping with the emotional aspects of cancer, the Cancer Center provides comprehensive information that parents need. Read More Cancer: Readjusting to Home and School If you've just finished a long hospital stay, you may have questions about reconnecting with friends and family. Get answers in this article for teens. Read More Side Effects of Chemotherapy and Radiation Side effects of cancer treatment can include flu-like symptoms, hair loss, and blood clotting problems. After treatment ends, most side effects go away. Read More Immunotherapy to Treat Cancer This promising new type of cancer treatment stimulates a person's immune system so it is better able to fight disease. Read More Caring for a Seriously Ill Child Taking care of a chronically ill child is one of the most draining and difficult tasks a parent can face. But support groups, social workers, and family friends often can help. Read More Chemotherapy Chemotherapy (chemo) is treatment with medicines that stop the growth of cancer cells. Read More Cancer Center Cancer is a serious illness that needs special treatment. Find out more about how kids can cope with cancer. Read More Chemotherapy Chemotherapy is a big word for treatment with medicines used to help people who have cancer. This medicine kills the cancer cells that are making the person sick. Read More Neutropenia Certain cancers, or cancer treatment, can weaken the immune system, requiring a child to stay home to avoid exposure to germs. Here are ways to help your child make the best of it. Read More Stem Cell Transplants Stem cells can develop into cells with different skills, so they're useful in treating diseases like cancer. Read More Cancer Center Visit our Cancer Center for teens to get information and advice on treating and coping with cancer. Read More Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor. © 1995-2021 KidsHealth®. All rights reserved. Images provided by The Nemours Foundation, iStock, Getty Images, Veer, Shutterstock, and Clipart.com.