Diagnosing Chronic Myelogenous Leukemia
Specialists at NYU Langone are experienced at identifying all types of leukemia. Some are acute, or fast growing, and others are chronic, or slow growing. Chronic myelogenous leukemia, commonly known as CML, is a slow-growing cancer in which the bone marrow—the spongy tissue inside bones that contains stem cells, which make new blood cells—produces too many immature white blood cells.
These immature cells accumulate in the bone marrow, and eventually appear in the blood. They interfere with the growth of healthy cells, including normal white blood cells, which fight infection; red blood cells, which carry oxygen throughout the body; and platelets, which help blood clot.
Chronic myelogenous leukemia is slightly more common in men than in women and tends to affect Caucasians more than other groups. Nearly half of people with CML are aged 65 or older. CML can also occur in children, but this is rare.
CML is caused by a genetic mistake that occurs in the chromosomes of the blood cells, when genes on two specific chromosomes move from one to another, changing the length of each. This creates a genetic mutation, or fusion gene, called BCR-ABL, also known as the Philadelphia chromosome. This new gene results in the production of an enzyme called tyrosine kinase, which promotes the activity and growth of immature white blood cells called myeloblasts in bone marrow.
It is not known why these genetic changes happen in some people, but risk factors include radiation exposure, including radiation therapy for other cancers.
CML progresses slowly, with the accumulation of white blood cells in the bone marrow, blood, and spleen over years. Sometimes, as the cancerous cells divide, new irregularities in chromosomes can cause acute myeloid leukemia (AML), a faster growing leukemia that requires more aggressive treatment.
Doctors may suspect you have CML if routine blood tests reveal elevated levels of both mature and immature white cells in the blood. Symptoms include fatigue, fever, and night sweats. Because leukemia can cause the spleen—which fights infection and filters blood—to swell, some people may feel fullness below the ribs on the left side. However, some people have no symptoms.
The different types of leukemia are treated differently, so it’s important to obtain the correct diagnosis. NYU Langone hematologist–oncologists, who specialize in diagnosing blood cancers, perform several tests to identify leukemia, determine the type, and find out how advanced it is.
Initial Blood Tests
During an initial exam, your oncologist draws blood to check the numbers of white cells, red cells, and platelets in it. In CML, white blood cell levels are often high and the platelet levels may be too high or too low.
Peripheral Blood Smear
This blood test provides information about the number, type, and shape of blood cells. It can determine if immature white blood cells called myeloblasts are present alone, indicating AML, or if there is an increase of all stages of white blood cells, which are normally found in the bone marrow, in the blood. This is a sign of CML.
Bone Marrow Aspiration and Biopsy
Leukemia starts in the bone marrow, so a doctor performs a bone marrow aspiration and biopsy to determine the type of leukemia a person has. During this procedure, which is done with a local anesthetic, your doctor uses two small needles to remove bone marrow fluid and tissue from the pelvic bone in the lower back. The cells are then sent to a laboratory for analysis by a hematopathologist, a doctor who specializes in diagnosing blood cancers.
A cell’s chromosomes contain DNA, which carries genetic information such as gender. An analysis of cells collected during bone marrow aspiration, called karyotyping, can identify the BCR-ABL genetic mutation, also called the Philadelphia chromosome, which is present in most people with CML.
At NYU Langone, your doctor orders a laboratory test called fluorescence in situ hybridization, which maps the genetic material in cells by using dyes that light up under a microscope. This test can identify the chromosomal changes that produce the Philadelphia chromosome. It can also pinpoint genetic changes that are too small to see in traditional laboratory tests.
A polymerase chain reaction test can detect the Philadelphia chromosome if a doctor isn’t able to identify it via fluorescence in situ hybridization. In this analysis, small pieces of DNA are amplified making it easier for doctors to identify and measure irregularities in a small number of cells. This means that even small amounts of leukemia can be identified.
Molecular Profiling Studies
A laboratory test called a quantitative reverse transcriptase polymerase chain can determine the amount of BCR-ABL in the blood. This test, performed with blood and bone marrow samples the doctor retrieved during aspiration, allows doctors to determine the cancer’s likelihood for responding to certain treatments.
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