When leukemic blasts appear in the bone marrow, they multiply rapidly and do not develop into normal WBCs. They begin to crowd out the normal cells that grow from healthy blasts into mature WBCs. After accumulating in the bone marrow and lymph nodes, leukemic blasts spill over into the blood and, if left unchecked, may invade the central nervous system (CNS)—which includes the brain and spinal cord—and other organs, such as the liver and spleen.

When leukemic blasts begin to fill the bone marrow, production of healthy RBCs, platelets, and WBCs cannot be maintained. As the number of normal blood cells decreases, symptoms appear. Low RBC counts cause fatigue and pale skin. Low platelet counts may result in bruising and bleeding problems. And if mature WBCs are crowded out by blasts, the child will have little or no defense against infections.

Our 3-year-old daughter, Charlotte, changed from a quiet but friendly preschooler to a fearful, withdrawn one in just a few months. She didn’t want to go to preschool, see her friends, or play outside. She would lie on the couch a lot. She had bruises, and we didn’t know why because she hadn’t been playing. She didn’t look well, but the doctor couldn’t find anything wrong. She became pale and didn’t sleep well. Finally, the doctor took a blood sample, and when he called me on the phone to tell me she had leukemia, I dropped to my knees and couldn’t get up.