Normally, the bone marrow makes blood stem cells (immature cells) that become mature blood cells over time. A blood stem cell may become a myeloid stem cell or a lymphoid stem cell. A lymphoid stem cell becomes a white blood cell.

A myeloid stem cell becomes one of three types of mature blood cells:

Red blood cells that carry oxygen and other substances to all tissues of the body.
Platelets that form blood clots to stop bleeding.
Granulocytes (white blood cells) that fight infection and disease.

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Blood cell development; drawing shows the steps a blood stem cell goes through to become a red blood cell, platelet, or white blood cell. A myeloid stem cell becomes a red blood cell, a platelet, or a myeloblast, which then becomes a granulocyte (the types of granulocytes are eosinophils, basophils, and neutrophils). A lymphoid stem cell becomes a lymphoblast and then becomes a B-lymphocyte, T-lymphocyte, or natural killer cell. — Blood cell development. A blood stem cell goes through several steps to become a red blood cell, platelet, or white blood cell.

In CML, too many blood stem cells become a type of white blood cell called granulocytes. These granulocytes are abnormal and do not become healthy white blood cells. They are also calledleukemia cells. The leukemia cells can build up in the blood and bone marrow so there is less room for healthy white blood cells, red blood cells, and platelets. When this happens, infection, anemia, or easy bleeding may occur.

This summary is about chronic myelogenous leukemia. See the following PDQ summaries for more information about leukemia:

Signs and symptoms of chronic myelogenous leukemia include fever, night sweats, and tiredness.

These and other signs and symptoms may be caused by CML or by other conditions. Check with your doctor if you have any of the following:

Feeling very tired.
Weight loss for no known reason.
Night sweats.
Fever.
Pain or a feeling of fullness below the ribs on the left side.

Sometimes CML does not cause any symptoms at all.

Most people with CML have a gene mutation (change) called the Philadelphia chromosome.

Every cell in the body contains DNA (genetic material) that determines how the cell looks and acts. DNA is contained inside chromosomes. In CML, part of the DNA from one chromosome moves to another chromosome. This change is called the “ Philadelphia chromosome.” It results in the bone marrow making an enzyme, called tyrosine kinase, that causes too many stem cells to become white blood cells (granulocytes or blasts).

The Philadelphia chromosome is not passed from parent to child.

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Philadelphia chromosome; three-panel drawing shows a piece of chromosome 9 and a piece of chromosome 22 breaking off and trading places, creating a changed chromosome 22 called the Philadelphia chromosome. In the left panel, the drawing shows a normal chromosome 9 with the abl gene and a normal chromosome 22 with the bcr gene. In the center panel, the drawing shows chromosome 9 breaking apart in the abl gene and chromosome 22 breaking apart below the bcr gene. In the right panel, the drawing shows chromosome 9 with the piece from chromosome 22 attached and chromosome 22 with the piece from chromosome 9 containing part of the abl gene attached. The changed chromosome 22 with bcr-abl gene is called the Philadelphia chromosome. — Philadelphia chromosome. A piece of chromosome 9 and a piece of chromosome 22 break off and trade places. The bcr-abl gene is formed on chromosome 22 where the piece of chromosome 9 attaches. The changed chromosome 22 is called the Philadelphia chromosome.

Tests that examine the blood and bone marrow are used to detect (find) and diagnose chronic myelogenous leukemia.

The following tests and procedures may be used:

Physical exam and history : An exam of the body to check general signs of health, including checking for signs of disease such as an enlarged spleen. A history of the patient’s health habits and past illnesses and treatments will also be taken.
Complete blood count (CBC) with differential : A procedure in which a sample of blood is drawn and checked for the following:
- The number of red blood cells and platelets.
- The number and type of white blood cells.
- The amount of hemoglobin (the protein that carries oxygen) in the red blood cells.
- The portion of the blood sample made up of red blood cells.
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Complete blood count (CBC). Blood is collected by inserting a needle into a vein and allowing the blood to flow into a tube. The blood sample is sent to the laboratory and the red blood cells, white blood cells, and platelets are counted. The CBC is used to test for, diagnose, and monitor many different conditions.
Blood chemistry studies : A procedure in which a blood sample is checked to measure the amounts of certain substances released into the blood by organs and tissues in the body. An unusual (higher or lower than normal) amount of a substance can be a sign of disease in the organ or tissue that makes it.
Bone marrow aspiration and biopsy : The removal of bone marrow, blood, and a small piece of bone by inserting a needle into the hipbone or breastbone. A pathologist views the bone marrow, blood, and bone under a microscope to look for abnormal cells.Enlarge
Bone marrow aspiration and biopsy. After a small area of skin is numbed, a Jamshidi needle (a long, hollow needle) is inserted into the patient’s hip bone. Samples of blood, bone, and bone marrow are removed for examination under a microscope.
One of the following tests may be done on the samples of blood or bone marrow tissue that are removed:
- Cytogenetic analysis: A test in which cells in a sample of blood or bone marrow are viewed under a microscope to look for certain changes in the chromosomes, such as the Philadelphia chromosome.
- FISH (fluorescence in situ hybridization): A laboratory technique used to look at genesor chromosomes in cells and tissues. Pieces of DNA that contain a fluorescent dye are made in the laboratory and added to cells or tissues on a glass slide. When these pieces of DNA bind to specific genes or areas of chromosomes on the slide, they light up when viewed under a microscope with a special light.
- Reverse transcription polymerase chain reaction test (RT–PCR): A laboratory test in which cells in a sample of tissue are studied using chemicals to look for certain changes in the structure or function of genes.