What is acute lymphoblastic leukemia?
In people with ALL, something goes wrong with a type of blood stem cell called a lymphoblast. Instead of maturing into fully functioning lymphocytes — important immune-system cells — the lymphoblasts multiply out of control, and they don’t die off like normal blood cells do.
The underdeveloped (leukemic) cells can’t do their normal infection-fighting functions. They build up in your bone marrow and blood, crowding out the normal, healthy blood cells that your body needs.
Low levels of normal blood cells can lead to infection, anemia and excessive bleeding. The leukemic cells can travel around your body through your bloodstream and keep your organs from working right. ALL gets worse quickly if it is not treated, which makes it important to start treatment soon after diagnosis.
Understanding your bone marrow and blood
To understand leukemia, it helps to know the basics about your bone marrow and blood cells.
What are stem cells?
Stem cells are cells in your body that are able to turn into any kind of cell, such as a skin cell, liver cell, brain cell or blood cell. Stem cells that turn into blood cells are called hematopoietic stem cells, or blood stem cells.
Why are blood stem cells important?
When blood cells become old or damaged, they die, and blood stem cells make new blood cells to replace them. Blood stem cells are mainly found in bone marrow (the soft, spongy tissue inside your bones), but some are also found in the blood that circulates in your body. Blood stem cells make lymphoid stem cells and myeloid stem cells.
- Lymphoid stem cells make lymphoblasts. Lymphoblasts make several types of white blood cells.
- Myeloid stem cells make myeloblasts. Myeloblasts make white blood cells, red blood cells and platelets.
What do healthy blood cells do?
Healthy white blood cells, red blood cells and platelets are very important.
- White blood cells fight infection. The main types of white blood cells are B lymphocytes (B cells), T lymphocytes (T cells), natural killer (NK) cells and granulocytes.
- Red blood cells carry oxygen from your lungs to other parts of your body and take carbon dioxide back to your lungs to get rid of it (by breathing it out).
- Platelets make your blood clot and slow or stop bleeding.
What causes ALL?
We do not know what causes ALL. The disease is more common in children aged 5 or younger, and the risk is also higher after age 50. It is more common in males than females, and it is more common in white people than Black people.
- There are a few risk factors we know about:
- Being exposed to high levels of radiation
- Being exposed to certain chemicals, such as chemotherapy or benzene
- Having certain viral infections, although this is more common outside the U.S.
- Having certain genetic conditions, such as Down syndrome
- Having an identical twin who develops ALL as an infant or young child
However, keep in mind that many people who develop ALL do not have any of these risk factors, and most people with these risk factors do not develop the disease.