Chronic myeloid leukemia (CML) starts in the blood-forming cells in the bone marrow and spreads to the blood. The symptoms and treatment options can vary according to the stage of CML.

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Doctors may sometimes refer to the disease as chronic myelogenous leukemia, chronic granulocytic leukemia, or chronic myelocytic leukemia.

Keep reading to learn more about CML, including how it compares with other types of leukemia.

CML is a type of blood cancer that starts in the blood-forming cells of the bone marrow. According to the American Cancer Society, it accounts for about 15% of adult cases of leukemia but rarely affects children.

The Leukemia & Lymphoma Society (LLS) adds that CML is one of the four most common forms of leukemia in adults.

It also notes that there are three phases of CML:

  • Chronic phase: Doctors often diagnose people during this phase, when the disease typically responds well to treatment. Although many people do not have symptoms at this stage, doctors may detect the cancer if they order blood tests for the person for another health condition.
  • Accelerated phase: This phase occurs if the chronic phase is untreated. The cancer grows faster, and a person may experience some symptoms, such as fatigue and weight loss.
  • Blast (or blastic) phase: Similar to the acute form of myeloid leukemia, this phase produces a range of symptoms. The cancer may spread outside of the bone marrow and blood.

CML vs. chronic lymphocytic leukemia

CML and chronic lymphocytic leukemia (CLL) are two different types of chronic leukemia. CLL is the most common form of chronic leukemia.

Both CML and CLL develop slowly and may not present with symptoms right away.

The main difference between the types is what cells they affect. CLL develops in white blood cells called lymphocytes, whereas CML starts in the myeloid cells, which form red blood cells, platelets, and white blood cells.

CML vs. acute myeloid leukemia

The National Cancer Institute (NCI) notes that acute myeloid leukemia (AML) is the most common type of acute leukemia in adults. It spreads quickly, which means that early diagnosis and treatment can have a significant effect on treatment outcomes.

CML is slower to develop, although in the later phases, it can grow and spread similarly to AML.

In both cases, changes in the cells of bone marrow cause the formation of abnormal red or white blood cells or platelets. Both AML and CML require treatment, although the options can vary among individuals depending on their age and overall health.

The symptoms of CML may differ among the phases. The LSS states that during the chronic phase, a person may not experience any symptoms.

When symptoms do occur, they are nonspecific, meaning that they overlap with those of many different conditions. Due to this, a person who does experience symptoms may not associate them with CML.

Some common symptoms include:

  • night sweats
  • weakness
  • fever
  • feeling full after eating a small meal
  • fatigue
  • weight loss
  • pain in the bones
  • pain or fullness in the stomach
  • enlarged spleen

The LLS adds that many of the symptoms occur due to anemia or other CML-related issues.

The American Cancer Society notes that most cases of CML result from mutations or changes within the DNA of cells. In most cases of CML, chromosomes 9 and 22 “swap” part of their code.

This swapping of the code, known as translocation, causes chromosome 22 to be shorter than it would be otherwise. The shortened chromosome is called the Philadelphia chromosome, and it is present in nearly all people living with CML.

The swapped chromosomes lead to the creation of a new, cancerous gene known as BCR-ABL. The new gene creates the BCR-ABL protein, which is responsible for the growing and rapid dividing of CML cells.

Certain risk factors can make it more likely that a person will develop CML.

The American Cancer Society lists the following risk factors:

  • Age: A person’s risk increases as they get older.
  • Radiation exposure: Exposure to high degrees of radiation from a nuclear reactor accident or atomic bomb blast increases the risk of CML.
  • Sex: Males are more likely than females to develop CML.

CML often does not cause symptoms in the early phase of the disease. However, a doctor may discover the cancer if a routine blood examination reveals an abnormal white blood cell count.

If CML does present with symptoms, these will be nonspecific, and the doctor will need to order tests to confirm the condition and rule out other causes.

Tests that they may order to confirm a diagnosis of CML include:

  • Complete blood count (CBC) with differential: This test reveals the different types of white blood cells present, as well as providing red blood cell and platelet counts.
  • Bone marrow aspiration and biopsy: Doctors use this to examine abnormalities in bone marrow cells.
  • Peripheral blood smear: This test allows doctors to determine the number of each type of blood cell and their shapes and sizes.
  • Cytogenetic analysis: This analysis checks for chromosome abnormalities in the bone marrow.
  • Quantitative polymerase chain reaction (qPCR): A qPCR measures the amount of the BCR-ABL1 gene in the blood or bone marrow.
  • Fluorescence in situ hybridization (FISH): Doctors use FISH to study the genes and chromosomes in the cells.

There are multiple treatment options for CML. Several ongoing studies are also looking at new and better ways to treat the cancer.

Currently, treatments that the NCI identifies for use in CML include:

  • chemotherapy
  • targeted therapy
  • high dose chemotherapy with stem cell transplant
  • surgery
  • donor lymphocyte infusion
  • immunotherapy

Various factors will determine a person’s treatment options, including the phase of CML they are in and their age and overall health. A treatment team will work with the individual to develop a plan that works best for them.

Chronic phase treatment

According to the NCI, doctors often suggest the following treatments for people who receive a diagnosis while they are in the chronic phase of CML:

  • chemotherapy
  • high dose chemotherapy with donor stem cell transplant
  • targeted therapy using a tyrosine kinase inhibitor
  • splenectomy
  • a new treatment as part of a clinical trial

Accelerated phase treatment

Common treatments for the accelerated phase of CML include:

  • targeted therapy using a tyrosine kinase inhibitor
  • high dose chemotherapy
  • donor stem cell transplant
  • tyrosine kinase inhibitor therapy and then donor stem cell transplant
  • immunotherapy (interferon) with or without chemotherapy
  • transfusion therapy
  • a new treatment as part of a clinical trial

Blastic phase treatment

The blastic phase is a much more aggressive version of CML. Treatment may involve:

  • high dose chemotherapy
  • targeted therapy using tyrosine kinase inhibitors such as imatinib mesylate (Gleevec), dasatinib (Sprycel), or nilotinib (Tasigna)
  • donor stem cell transplant
  • chemotherapy to help improve quality of life and relieve symptoms
  • participation in clinical trials

In general, the sooner a person receives treatment for CML, the better their outcome. However, a person’s age and overall health will play a part in determining their outcome, as will the phase of CML at diagnosis.

The American Cancer Society notes that the most effective drugs for CML treatment only became available in 2001, so there is not yet much data on life expectancy when taking these medications. However, most people who have received these treatments are still alive.

The researchers behind a large study published in 2012 reported the following CML survival rates since 2001:

  • chronic phase: 87% survival rate after 8 years
  • accelerated phase: 75% survival rate after 8 years
  • blastic phase: median survival time of 6 months

Chronic myeloid leukemia (CML) is a chronic, slow-growing form of blood and bone marrow cancer. Many people receive a diagnosis during the chronic phase, giving them the best chance of a good outcome.

Several treatment options are available regardless of the phase of the disease. A person can work with their treatment team to develop the best treatment plan for them.