Chronic myeloid leukemia (CML)

What is chronic myeloid leukemia (CML)?

Leukemia is when the blood has an abnormal number of white blood cells. Blood is made up of white blood cells which fight infection, red blood cells which carry blood and platelets which help the blood to clot. If the body produces too many white blood cells, the other components of the blood started to get crowded out.

Chronic myeloid leukemia, or chronic myelogenous leukemia, starts in certain blood-forming cells of a person’s bone marrow. A genetic change occurs in the early stages of myeloid cells – those that make up red blood cells, platelets, and most of the white blood cells.

CML cells mature only partially, and in doing so the leukemia cells grow and divide, and start to build up in the bone marrow—even eventually spilling over into the blood. After a while, the leukemia cells can infiltrate other parts of the body.

CML is generally a slow-growing leukemia, but it can change into a fast-growing and acute leukemia that becomes hard to treat.

CML mostly occurs in adults, though it can occur in children, as well.

What are the symptoms of CML?

Because CML is, by name, a chronic leukemia, it may take quite a while before symptoms start to show—people often live many years without knowing they have CML. Unfortunately, chronic leukemias are often more difficult to treat than acute leukemias.

Some of the more common symptoms of CML are vague and caused by other things. They include:

  • Weakness
  • Fatigue
  • Abnormal white blood count
  • Weight loss
  • Fever
  • Bone pain
  • Night sweats
  • Pain or sense of “fullness” in the stomach
  • Feeling full after eating even a small amount of food
  • Mass under the left side of the ribs, an enlarged spleen

Additionally, people with CML do not make enough red blood cells, white blood cells that function properly, or platelets. This happens because the leukemia cells replace the regular blood-making cells in the bone marrow.

This shortage of blood cells can lead to other problems:

The shortage of red blood cells. It can cause weakness, tiredness, and shortness of breath.
The shortage of normal white blood cells. This particular shortage can heighten the risk of infection.
The shortage of a particular kind of white blood cell, the neutrophil. These cells are important in the fight of infection from bacteria. Those who are neutropenic are at high risk of getting serious bacterial infections.
The shortage of platelets, which can lead to excess bruising or bleeding. The opposite condition, thrombocytosis, is the production of too many platelets – but bruising and bleeding are an issue, as well, because the platelets do not function as they should.

How is CML treated?

You and your doctor will determine how to best treat your CML. Targeted therapy drugs are the main treatment for CML, but additional treatments may be necessary. These include:

  • Interferon
  • Chemotherapy
  • Radiation therapy
  • Surgery
  • Stem cell transplant

How is CML diagnosed?

Many people with CML don’t have any symptoms when it’s diagnosed—it’s typically found when a doctor orders blood tests for something completely unrelated or during a routine checkup.

If your doctor suspects you may have leukemia, you will have blood and bone marrow samples taken and tested; blood is usually drawn from a vein in the arm, bone marrow is extracted during a procedure called a bone marrow aspiration and biopsy.

Bone aspiration and biopsy

The bone marrow aspiration and biopsy are done at the same time. Samples are generally taken from the back of the pelvic bone (hip), or sometimes from the sternum (breastbone).

These samples are sent to a lab where they examined for leukemia cells.

Lab tests

There are several lab tests that may be used to determine whether you have CML or how advanced the disease may be.

How is CML staged?

Most cancer is staged according to the size of the tumor and the cancer’s progression, or how much it has spread. Stages are helpful in determining the prognosis, or outlook, for the patient.

CML, however, is a disease of the bone marrow and so it isn’t staged like most other cancers. The prognosis depends on other things, such as the phase of the disease, age of the patient, blood counts, and whether the spleen is enlarged.

There are three phases of CML. The phases are determined by the number of immature white blood cells, or myeloblasts, that are found in the blood or bone marrow.

Chronic phase

These patients have a small amount—generally less than 10 percent—of myeloblasts in their blood or bone marrow, have fairly mild symptoms, and usually respond to standard treatments. Most patients are in the chronic phase when they are diagnosed.

Accelerated phase

Patients may be in the accelerated phase if they experience any of the following:

  • More than 10 percent but less than 20 percent myeloblasts in the blood or bone marrow
  • High count of blood basophil, or granular cells—making up more than 20 percent of the white blood count
  • High white blood cell counts that don’t respond to treatment
  • Very high or very low platelet counts not caused by treatment
  • New chromosome changes in the leukemia cells

Patients in this phase may also experience fever, loss of appetite, and weight loss. CML in this phase doesn’t respond as well to treatment as it does in the chronic phase.

Blast phase

Patients in this phase typically have more than 20 percent myeloblasts. These myeloblasts often spread to tissues and organs beyond the bone marrow. Patients in this phase will also likely experience fever, loss of appetite and weight loss. Here, CML acts like an aggressive acute leukemia.

How is prognosis determined?

There are several factors that can help determine a patient’s prognosis, or outlook for survival, many of which can be helpful when choosing treatment. Things that may be linked to shorter survival time are:

  • Accelerated, or blast, phase
  • Enlarged spleen
  • Areas of bone damage from the leukemia’s growth
  • An increased number of basophils and eosinophils (certain types of cells) in blood samples
  • Very high or very low platelet counts
  • Age 60 or older
  • Several chromosomal changes in the CML cells

Each of these factors is used in a scoring system, such as the Sokal system or the Euro score, to put patients into low-, intermediate-, or high-risk groups.

CML risk factors

What causes CML?

With many cancers, there are risk factors that you can control to increase or decrease your chances of getting the disease. Smoking or prolonged exposure to radon can increase your chances of getting lung cancer, for example. Over-exposure to damaging ultra-violet rays, like you’d get with sunburn, can increase your chances of skin cancer.

But risk factors aren’t a guarantee: Not everyone who smokes gets lung cancer, and not everyone who has lung cancer has been exposed to any of the risk factors.

There are few risk factors with CML, but they include:

Radiation exposure

Being exposed to high-dose radiation (such as being a survivor of a nuclear reactor accident).


The risk of getting CML increases with age.


Men are more likely than women to get CML, though it’s not known why.

Should I get screened for CML?

Unfortunately, there are no screening tests routinely available to detect CML in the early stages. However, CML is sometimes detected when certain symptoms show up in routine blood tests done for other reasons. For example, a person’s white blood cell count may be very high, even if there are no other symptoms. That may lead to other tests in which CML may be found.

Last reviewed: 
December 2017
Alternative Names: 
Chronic Myelogenous Leukemia

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