Leukemia is cancer that starts in the tissue that forms blood. Most blood cells develop from cells in the bone marrow called stem cells. In a person with leukemia, the bone marrow makes abnormal white blood cells. The abnormal cells are leukemia cells. Unlike normal blood cells, leukemia cells don’t die when they should. They may crowd out normal white blood cells, red blood cells, and platelets. This makes it hard for normal blood cells to do their work.
Adult leukemias are expected to account for more than 3.4 percent of all new cancer cases in 2021, or about 61,090 new cases as well as an estimated 23,660 deaths, according to federal statistics.
The four most common types of leukemia are:
- Acute lymphoblastic leukemia (ALL): ALL affects lymphoid cells and grows quickly. Leukemic blast cells usually collect in the bone marrow and blood.
- Acute myelogenous leukemia (AML): AML affects myeloid cells and grows quickly. Leukemic blast cells collect in the bone marrow and blood.
- Chronic lymphocytic leukemia (CLL): CLL affects lymphoid cells and usually grows slowly. Blood tests show an increase in the number of white blood cells. The abnormal cells work almost as well as the normal white blood cells.
- Chronic myelogenous leukemia (CML): CML affects myeloid cells and usually grows slowly at first. Blood tests show an increase in the number of white blood cells. The abnormal blood cells work adequately. There may be a small number of leukemic blast cells in the bone marrow.
Source: National Cancer Institute