JMML is cancer of immature WBCs called monocytes, which would normally develop into healthy macrophages (see Figure 5–1). Macrophages float in the blood, killing foreign organisms, removing dead cells, and helping the body fight infection.

When cancerous monocytes appear in the bone marrow, they multiply rapidly and lose their ability to develop into mature macrophages. They begin to crowd out the healthy stem cells that would mature into WBCs, RBCs, and platelets. When this happens, infection, anemia, or bleeding may occur. After accumulating in the bone marrow, cancerous monocytes spill over into the blood and invade other organs such as the spleen, liver, and lungs.

Figure 5–1: JMML is a disease of the monocytes

Because treatments for the four main types of childhood leukemia are very different, it is crucial that sophisticated laboratory studies be performed at diagnosis to identify the type of leukemia and the best treatment.

My daughter was diagnosed with JMML at the age of 27 months. Although it is a chronic leukemia, it is particularly fast moving. My daughter had a partial match (my husband’s sister as donor) stem cell transplant four months after she was diagnosed. Today, she is eight years post-transplant, is in the fourth grade, and is the absolute joy of my life.