This page was reviewed under our medical and editorial policy by
Maurie Markman, MD, President, Medicine & Science
This page was updated on May 26, 2022.
Also known as chronic myelogenous leukemia, chronic myeloid leukemia (CML) is a form of cancer that affects the bone marrow and blood. It begins in the blood-forming cells of the bone marrow and then, over time, spreads to the blood. Eventually, the disease spreads to other areas of the body.
Typically, being categorized as chronic indicates that this type of leukemia spreads and grows slowly. However, CML can change from slow progressing into a rapidly growing, acute form of leukemia that can spread to almost any organ in the body.
Unlike the three other main types of leukemia, CML has a significant difference that sets it apart from the rest. An abnormality in the chromosome known as the Philadelphia chromosome (Ph chromosome) has been known to cause CML.
Chromosomes are structures in cells that contain genes, which give instructions to the cells. The Ph chromosome is an abnormality that occurs when a piece of chromosome 22 breaks off and attaches to the end of chromosome 9, which also breaks off and attaches to chromosome 22.
The breaks in both chromosomes cause the BCR and ABL genes, which combine to create the cancer gene. The link between the Ph chromosome and CML was discovered around 1960.
Symptoms of CML include:
Most cancers are classified by stage based on the size of the tumor and whether it has spread. However, chronic myeloid leukemia is classified differently, using phases rather than stages, because it is a cancer of the bone marrow.
The phases are based on disease progression as well as factors such as your age, your blood counts and whether your spleen is enlarged. The three phases of CML are called:
The defining factor of each phase is primarily the number of blasts, or immature white blood cells, in your blood or bone marrow. Your cancer care team may also have additional criteria to distinguish between the different phases. However, below are the generally agreed-upon definitions of each phase.
This is the first, early phase of CML:
At this phase, CML often responds well to standard treatments.
This phase is characterized by one or more of these findings:
The response to treatment is not as good as in the chronic phase.
Treatment for CML may include radiation therapy, chemotherapy, stem cell transplant and/or immunotherapy. Your integrated team of leukemia experts will answer your questions and recommend treatment options based on your unique diagnosis and needs.
A very targeted treatment approach for the early phase of chronic myeloid leukemia involves oral drugs known as tyrosine kinase inhibitors (TKIs). These include:
If one TKI drug doesn’t work, your doctor may switch to another. You also may be given an increased dose of the drug. However, the higher the dose, the greater the side effects can be.
If you can’t take TKIs, your doctor may try interferon or chemotherapy.
The five-year survival rate tells you what percentage of patients diagnosed with CML were alive five years after their initial diagnosis based on past data. Thanks to scientific advances and newer targeted drugs such as imatinib, the survival rate for patients with CML has improved dramatically, from 22 percent in the mid-1970s to 72 percent, according to the American Society of Clinical Oncology. A recent study found that 90 percent of patients who took imatinib consistently lived at least five years.
Next topic: What is hairy cell leukemia?