Leukemia is a cancer of the blood. Leukemia begins when healthy blood cells change and grow out of control. Acute lymphocytic leukemia (ALL) is a cancer of the immature lymphocytes. Lymphocytes are a type of white blood cell involved in the body’s immune system. ALL is also called acute lymphoid leukemia or acute lymphoblastic leukemia. Acute means that the disease begins and gets worse quickly. People with ALL usually need immediate treatment. ALL is most common in young children and adults older than 50, but people of any age can develop ALL.
Lymphocytes are made in the bone marrow, the spongy, red tissue in the inner part of the large bones. Lymphocytes are found in the blood, lymph nodes, and spleen. Healthy lymphocytes fight bacterial and viral infections. In people with ALL, new lymphocytes do not develop into mature cells, but stay as immature cells called lymphoblasts.
There are 3 different types of lymphocytes: B cells, T cells, and natural killer (NK) cells.
- B cells make antibodies.
- T cells fight infections by activating other cells in the immune system and by destroying infected cells.
- NK cells fight microbes and cancer cells.
About 85% of people with ALL have the B-cell subtype and about 15% have the T-cell type. The NK-cell subtype is quite rare.
In people with ALL, the abnormal cells crowd other types of cells in the bone marrow. This prevents the production of the following cells:
- Red blood cells, which carry oxygen
- Other types of white blood cells
- Platelets, which are parts of the blood needed for clotting
This means that people with ALL may have problems related to having too few healthy blood cells, including:
- Anemia, from not enough red blood cells
- Infections because they do not have enough of the type of white blood cells called neutrophils that fight bacteria
- Increased risk of bruises or bleeding because of a low level of platelets
Lymphoblasts may also collect in a person’s lymphatic system and cause swelling of the lymph nodes. Some cells may invade other organs, including the brain, liver, spleen, thymus, or the testicles in men.
Unlike other types of cancer, the spread of ALL to other parts of the body does not mean the cancer is in an advanced stage. Acute leukemia is usually found throughout the body when it is diagnosed and it may still be cured.
This section is about ALL in adults. Read about childhood ALL.