Leukemia is a cancer that disrupts the normal development of blood cells. Inside most of your bones is a soft spongy material called bone marrow in which blood stem cells (immature blood cells) are produced. A blood stem cell becomes one of two types of stem cells: myeloid or lymphoid, each of which matures into different kinds of blood cells.
Myeloid stems cells become one of the following:
- Red blood cells that carry oxygen to and from the tissues in your body
- Platelets that help your blood to clot to control bleeding
- Infection-fighting white blood cells known as granulocytes
Lymphoid stem cells become lymphoblasts, which mature into one of the following types of white blood cells:
- B lymphocytes (B cells), which produce antibodies that identify and destroy bacteria and viruses
- T lymphocytes (T cells), which fight against viruses and stimulate B cells to produce antibodies
- Natural killer (NK) cells, which kill tumor cells and disease-carrying microorganisms
Acute lymphocytic leukemia (ALL) disrupts the normal development of these cells. With ALL, lymphoid blast cells multiply at a very high rate, but they never develop into fully functioning B lymphocytes or T lymphocytes. They also don’t die off like normal bloods cells do. As a result, these leukemic cells begin to accumulate and crowd out other healthy blood cells. This results in the reduction of normal blood cell numbers, which in turn can cause infection, anemia and excessive bleeding. And as these leukemia cells move out of the bone marrow and into the bloodstream, they can disrupt functions of other parts of the body, including the liver, spleen, lymph nodes, mouth, gums and central nervous system.
About 85 percent of ALL cases are of B-cell type (precursors of B cells), while the remaining 15 percent are of T-cell type (precursors of T cells).