Leukemia--Chronic Myeloid (Myelogenous) Overview

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What Is Leukemia - Chronic Myeloid (CML)? TOPICS

What is chronic myeloid leukemia?

Leukemia is a type of cancer that starts in cells that form new blood cells. These cells are found in the soft, inner part of the bones called the bone marrow. Normal bone marrow, blood and lymph tissue

To understand the different types of leukemia, it helps to know a little about the blood and lymph systems. Any blood-forming cell can turn into a leukemia cell. Once that happens, the cell can grow and divide to form many new cancer cells. These cells can take over the bone marrow, spill out into the bloodstream, and spread to other organs. The build up of these cells can lead to a shortage of normal blood cells. Having too many leukemia cells can keep other cells in the body from working the way they should.

Lymph system

The immune system is made up mainly of lymph tissue (also known as lymphatic or lymphoid tissue). The main cell type that forms lymph tissue is the lymphocyte, a kind of white blood cell. (White blood cells help the body fight infections.) The 2 main types of lymphocytes are called B cells and T cells. Normal T cells and B cells do different jobs within the immune system in order to find and kill germs.

  • B lymphocytes protect the body from invading germs.
  • T lymphocytes destroy cells that are infected with viruses and help regulate the immune system.

Bone marrow

Bone marrow is the soft inner part of some bones like the skull, shoulder blades, ribs, pelvis, and backbones. Bone marrow is made up of blood-forming cells, fat cells, and tissues that help cells grow.

The cells that make blood are called blood stem cells. These stem cells only make new blood-forming cells. They are different from embryonic stem cells because they cannot make any other kinds of cells.

Stem cells divide to make new stem cells. But they also go through a series of changes to make blood cells. During this process they can become red blood cells, white blood cells, or platelets.


Platelets aren't whole cells but rather are pieces of large cells that plug up holes in blood vessels caused by cuts or bruises. A person with a shortage of platelets can bruise or bleed easily.

Red blood cells

Red blood cells carry oxygen from the lungs to all other cells in the body. They also carry away carbon dioxide, a cell waste product. Not having enough red blood cells is called anemia and makes a person feel weak, short of breath, and tired.

White blood cells

White blood cells help the body fight infections. Lymphocytes are one type of white blood cell, but there are other types that together are called myeloid cells. In chronic myeloid leukemia, it’s the cells that become myeloid cells that become cancerous.

Chronic myeloid leukemia

Chronic myeloid leukemia (CML) is also known as chronic myelogenous leukemia. In CML, leukemia cells tend to build up in the body over time. In many cases, people don't have any symptoms for at least a few years. CML can also change into a fast-growing, acute leukemia that invades almost any organ in the body. Most cases of CML occur in adults, but very rarely it is found in children. As a rule, their treatment is the same as for adults.

Leukemia is different from other types of cancer that start in organs such as the lungs, colon, or breast and then spread to the bone marrow. Cancers that start elsewhere and then spread to the bone marrow are not leukemia.

CML isn’t the only kind of leukemia. There are 4 main types of leukemia:

Knowing the exact type can help doctors better predict each patient's outlook (prognosis) and select the best treatment.

The rest of this document contains information about chronic myeloid leukemia (CML) in adults only. Information about the other types of adult leukemia is covered in different American Cancer Society documents. For information about leukemia in children, please see the document Childhood Leukemia Overview.

Last Medical Review: 08/13/2013
Last Revised: 02/10/2014