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What Is Chronic Myeloid Leukemia?
Chronic myeloid leukemia (CML), also called chronic myelogenous leukemia, is a cancer that begins in certain blood-forming cells of the bone marrow—the soft, spongy tissue inside bones where blood cells are made.
CML most often affects adults, but in rare cases it can occur in children as well. When it does, treatment approaches are generally the same as those used for adults.
All leukemias, including chronic myeloid leukemia (CML), begin in the blood-forming cells of the bone marrow. Normally, these cells grow, do their jobs, and then die. When a cell develops mutations in its DNA, it can become a leukemia cell. Unlike healthy cells, leukemia cells don’t mature the way they should and don’t die when expected. Instead, they build up in the bone marrow, crowding out normal cells.
Over time, these leukemia cells move into the bloodstream, increasing the number of white blood cells and sometimes spreading to other organs. This can interfere with how the body functions. Identifying the exact type of leukemia is an important step in guiding treatment and understanding a patient’s outlook.
What does “chronic” mean?
Leukemia is classified as either acute or chronic. Acute leukemia grows quickly, while chronic leukemia progresses more slowly.
CML is a chronic leukemia. In chronic leukemia, cells partly mature but never become fully healthy white blood cells. They may appear fairly normal, but they don’t fight infection as effectively. These cells also live longer than they should and continue to accumulate, crowding out healthy blood cells. Because of its slow progression, chronic leukemia may not cause problems right away. Many people live with it for years, though chronic leukemias are often more difficult to cure than acute leukemias.
What does “myeloid” mean?
Leukemia is also grouped as either lymphocytic or myeloid, based on the type of bone marrow cell where the cancer begins.
- Lymphocytic leukemias start in cells that would normally become white blood cells called lymphocytes.
- Myeloid leukemias start in early myeloid cells, which develop into red blood cells, most types of white blood cells (other than lymphocytes), or platelet-producing cells.
CML is a myeloid leukemia. It begins in early myeloid cells and causes abnormal growth of these cells over time.
Chronic Myeloid Leukemia Cancer Prognosis and Survival Rates
According to the American Cancer Society, an estimated 9,560 people will be diagnosed with chronic myeloid leukemia (CML) in 2025, including about 5,610 men and 3,950 women. Approximately 1,290 people (740 men and 550 women) are expected to die from the disease.
CML represents about 15% of all new leukemia cases in the U.S. each year. Over a lifetime, about 1 in 500 people will develop CML.
The average age at diagnosis is 66 years, and while CML primarily affects older adults, about 2% of cases occur in people younger than 20.
Why Come to CU Cancer Center for Chronic Myeloid Leukemia Cancer
The CU Cancer Center is home to world-class leukemia care teams. The team’s research has led to many different breakthroughs in how to treat cancers that affect the blood and bone marrow. As the only National Cancer Institute Designated Comprehensive Cancer Center in Colorado and one of only four in the Rocky Mountain region, CU Cancer Center doctors provide multidisciplinary, patient-centered care, and innovative treatments unavailable at most other medical centers in the country.
CU Cancer Center doctors are the only physicians in a 500-mile radius who are part of the National Comprehensive Cancer Network (NCCN) advisory panel. The NCCN establishes treatment guidelines that doctors across the U.S. use as a reference.
There are over 30 leukemia clinical trials currently being offered by CU Cancer Center members, giving patients many different new treatment options as well as the standard care choices.
→ Two Studies by CU Cancer Center Researchers Explore Link Between Inflammation and Leukemia
Learn more about the Center for Cancer and Blood Disorders, diagnosis and treatment options for pediatric leukemia from our clinical partners at Children’s Hospital Colorado.
Risk Factors
Having one or even several risk factors does not mean someone will definitely develop CML. Many people with risk factors never get the disease, while others may be diagnosed without having any known risk factors.
Here’s what we know about the risk factors for CML:
Age
- CML can occur at any age, but the risk increases with age.
- The average age at diagnosis is about 66 years.
- Around 7 in 10 people with CML are 55 or older.
Sex
- CML is slightly more common in men than women. The reason for this difference is not yet understood.
Radiation exposure
- High-dose radiation exposure (such as from an atomic bomb blast or nuclear reactor accident) increases the risk of developing CML.
- Radiation treatment for other cancers or conditions has also been linked to an increased risk.
- The impact of lower-dose radiation exposure (from medical imaging such as X-rays or CT scans) is less clear. If there is an added risk, it appears to be small. To be safe, doctors limit unnecessary radiation exposure, especially for children and pregnant women.
Other factors
- No other clear risk factors have been identified.
- CML does not appear to be linked to smoking, diet, chemical exposure, infections, or family history.
Prevention
Unlike some cancers, there is currently no known way to prevent most cases of chronic myeloid leukemia (CML). While healthy lifestyle choices can lower the risk of many other cancers, they don’t appear to affect the risk of developing CML.
The only potentially avoidable risk factor is exposure to high doses of radiation—a circumstance that applies to very few people.
Symptoms of Chronic Myeloid Leukemia
Chronic myeloid leukemia (CML) often develops slowly. Many people don’t notice symptoms at first, and the disease is sometimes found during a routine blood test before any symptoms appear.
When symptoms do occur, they may include:
- Tiredness or weakness
- Fever or night sweats
- Unexplained weight loss
- Loss of appetite or feeling full after eating only a small amount (caused by an enlarged spleen)
- Pain or fullness in the left side of the belly (from the spleen pressing against other organs)
- Bone or joint pain
- Pale skin (from anemia)
- Frequent infections or easy bruising/bleeding (from low blood cell counts)
Because these symptoms can be caused by many conditions, having them doesn’t necessarily mean you have CML. If you experience ongoing or unusual symptoms, it’s important to see a doctor for testing and diagnosis.
Diagnosis of Chronic Myeloid Leukemia (CML)
CML is often found during a routine blood test before symptoms appear. If your doctor suspects CML, several tests may be used to confirm the diagnosis and learn more about the disease:
- Blood tests – A complete blood count (CBC) measures the number and types of cells in your blood. People with CML often have very high white blood cell counts.
- Bone marrow test – A small sample of bone marrow is taken to check for leukemia cells.
- Cytogenetic and molecular tests – These specialized tests look for the Philadelphia chromosome and the BCR::ABL1 fusion gene, which confirm the diagnosis of CML.
- Physical exam – Your doctor may check for signs such as an enlarged spleen.
Together, these tests help your care team confirm the diagnosis, understand how advanced the disease is, and guide treatment.
Phases of CML
CML usually develops slowly, but it can progress to more aggressive stages over time. Doctors classify CML into three phases based on the number of abnormal cells and the presence of symptoms:
Chronic phase
- The earliest and most common phase at diagnosis.
- Symptoms may be mild or not noticeable.
- Blood tests show elevated white blood cells, but treatment with tyrosine kinase inhibitors (TKIs) is usually very effective.
Accelerated phase
- The disease begins to progress more quickly.
- Symptoms such as fatigue, fever, or an enlarged spleen may appear or worsen.
- Blood counts become harder to control.
Blast phase (blast crisis)
- The most advanced phase, when CML behaves more like an acute leukemia.
- A high number of immature white blood cells (blasts) are present.
- Symptoms can become severe, and treatment is more challenging.
Prognosis and Monitoring
The outlook for people with CML has improved dramatically with targeted treatments like TKIs. Many patients live long and full lives, managing CML as a chronic condition.
Ongoing monitoring is an important part of care. Your doctor will track your response to treatment with regular:
- Blood tests to measure blood cell counts
- Molecular tests to monitor levels of the BCR::ABL1 gene
- Bone marrow tests if needed, to assess disease activity
Treatments
Treatment for chronic myeloid leukemia (CML) has advanced dramatically in recent years. Today, many people with CML live long and healthy lives thanks to targeted therapies and other treatment options. The best treatment plan depends on your age, overall health, and the phase of CML.
Targeted Therapy
Targeted drugs called tyrosine kinase inhibitors (TKIs) are the main treatment for CML. These medicines work by blocking the abnormal BCR::ABL1 protein that drives the growth of leukemia cells. TKIs can help keep CML under control for many years, often allowing patients to live normal lives.
- Common TKIs include imatinib (Gleevec), dasatinib, nilotinib, bosutinib, and ponatinib.
- Most people take a TKI as a pill each day.
- Regular blood tests are needed to make sure the medicine is working and to check for side effects.
Chemotherapy
Before TKIs were developed, chemotherapy was the standard treatment for CML. Today, chemotherapy is used less often but may still play a role, especially if CML doesn’t respond to TKIs or if a stem cell transplant is being planned.
Stem Cell Transplant
A stem cell transplant (also called a bone marrow transplant) is the only known treatment that can potentially cure CML. It involves replacing diseased bone marrow with healthy stem cells from a donor. Because it carries serious risks, transplants are usually considered only if TKIs are not effective or if CML has progressed to a more advanced phase.
Clinical Trials
Researchers are studying new drugs and treatment strategies for CML. Taking part in a clinical trial may give patients access to promising therapies not yet widely available.
Monitoring and Living With CML
CML is often a long-term condition that requires ongoing care. Most patients take TKIs for many years and may need frequent follow-up visits and testing. With proper treatment, many people with CML can manage the disease as a chronic condition and maintain a good quality of life.
The University of Colorado (CU) Cancer Center partners with UCHealth, Children’s Hospital Colorado, and Rocky Mountain Regional VA to provide clinical care. Please make an appointment with one of our clinical partners to be seen by a CU Cancer Center doctor.
UCHealth Cancer Care - Anschutz Medical Campus
1665 Aurora Court Anschutz Cancer Pavilion
Aurora, CO 80045
720-848-0300
UCHealth Cherry Creek Medical Center
100 Cook Street
Denver, CO 80206
720-848-0000
UCHealth Cancer Center - Highlands Ranch
1500 Park Central Drive
Highlands Ranch, CO 80129
720-516-1100
UCHealth Lone Tree Medical Center
9548 Park Meadows Drive
Lone Tree, CO 80124
720-848-2200
Children's Hospital Colorado:
13123 East 16th Avenue
Aurora, CO 80045
720-777-6740
Rocky Mountain Regional VA Medical Center:
1700 North Wheeling Street
Aurora, CO 80045-7211
303-399-8020
Latest in Leukemia from the CU Cancer Center
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Information reviewed by Daniel Pollyea, MD in September 2025.