Normally, the bone marrow makes blood stem cells (immature cells) that become mature blood cells over time. A blood stem cell may become a myeloid stem cell or a lymphoid stem cell.
A myeloid stem cell becomes one of three types of mature blood cells:
Red blood cells that carry oxygen and other substances to all tissues of the body.
Platelets that form blood clots to stop bleeding.
Granulocytes (white blood cells) that fight infection and disease.
A lymphoid stem cell becomes a lymphoblast cell and then one of three types of lymphocytes (white blood cells):
B lymphocytes that make antibodies to help fight infection.
T lymphocytes that help B lymphocytes make the antibodies that help fight infection.
Natural killer cells that attack cancer cells and viruses.
Blood cell development. A blood stem cell goes through several steps to become a red blood cell, platelet, or white blood cell.
In ALL, too many stem cells become lymphoblasts, B lymphocytes, or T lymphocytes. These cells are also called leukemia cells. These leukemia cells are not able to fight infection very well. Also, as the number of leukemia cells increases in the blood and bone marrow, there is less room for healthy white blood cells, red blood cells, and platelets. This may cause infection, anemia, and easy bleeding. The cancer can also spread to the central nervous system (brain and spinal cord).
This summary is about adult acute lymphoblastic leukemia. See the following PDQ summaries for information about other types of leukemia: