Juvenile myelomonocytic leukemia (JMML) is a rare childhood cancer that occurs more often in children younger than 2 years. Children who have neurofibromatosis type 1 and males have an increased risk of juvenile myelomonocytic leukemia.
In JMML, the body tells too many blood stem cells to become two types of white blood cells called myelocytes and monocytes. Some of these blood stem cells never become mature white blood cells. These immature white blood cells are called blasts. Over time, the myelocytes, monocytes, and blasts crowd out the red blood cells and platelets in the bone marrow. When this happens, infection, anemia, or easy bleeding may occur.
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