Cancer is a disease in which cells grow in an abnormal way. They are supposed to divide in a controlled way to replace old or damaged cells. With leukemia, blood cells grow and divide quickly, making more than are needed.

Normal Blood Cells and the Development of Leukemia

All blood cells start in the bone marrow as stem cells. Stem cells mature into many types of blood cell that have certain roles in the body. These are:

  • Red blood cells—Carry oxygen from the lungs to the organs and cells of the body.
  • Platelets—Fix broken blood vessels by making the blood clot to stop bleeding.
  • White blood cells—Helps the body fight infection and disease.

White Blood Cells

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New, healthy cells are made in the bone marrow. This keeps the number of blood cells in a healthy range. With leukemia, too many abnormal cells are made and they crowd out the bone marrow. This makes it hard for new, healthy cells to be made. Cancer moves around the body in the blood and lymph streams. This keeps organs like the spleen, liver, brain, and lymph nodes from working as they should.

Cancer Cell Growth

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Types of Leukemia

Leukemia is grouped by how fast it grows and the type of blood cell affected. The groups are:

  • Acute —Cells are not fully formed. They grow and spread quickly. The effects on the body happen fast.
  • Chronic —Cells are mature and fully formed, meaning they look like normal cells. However, they do not work like they should. Chronic leukemia may not be noticed until symptoms appear. This can take years. In some people, it is found during a routine blood test.

Leukemia is also grouped by the bone marrow cells it starts in:

  • Myeloid —Affects myeloid cells which grow into certain types of white blood cells, red blood cells, and platelets.
  • Lymphocytic or lymphoblastic —Affects lymphoid cells that normally grow into a type of white blood cell called a lymphocyte.

Common types of leukemia include:

  • Acute lymphoblastic leukemia (ALL)—Most common type of leukemia in young children, but it can happen in older adults.
  • Acute myeloid leukemia (AML)—Found in both adults and children.
  • Chronic lymphocytic leukemia (CLL)— Most common in older adults. It can happen in younger adults and in children, but this is rare.
  • Chronic myeloid leukemia (CML)—Found mainly in adults, but also in a very small number of children.

Acute lymphoblastic leukemia/lymphoma (ALL). EBSCO DynaMed Plus website. Available at:

Acute myeloid leukemia (AML). EBSCO DynaMed Plus website. Available at:

Chronic lymphocytic leukemia (CLL)/small lymphocytic leukemia (SLL). EBSCO DynaMed Plus website. Available at:

Chronic myeloid leukemia. EBSCO DynaMed Plus website. Available at:

Leukemia. Leukemia & Lymphoma Society website. Available at:

Leukemia—patient version. National Cancer Institute website. Available at:

Overview of leukemia. Merck Manual Professional Version website. Available at:

Last reviewed December 2020 by EBSCO Medical Review Board Mohei Abouzied, MD, FACP  Last Updated: 3/14/2021