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Phases of Chronic Myeloid Leukemia: Chronic, Accelerated, Blast

Posted on April 14, 2022
Medically reviewed by
Richard LoCicero, M.D.
Article written by
Maureen McNulty

If you are diagnosed with chronic myeloid leukemia (CML), also called chronic myelogenous leukemia, your doctor will tell you what phase your leukemia is in. Your phase helps determine your treatment and prognosis, or outlook.

Types of cancer that lead to solid tumors are classified using stages that describe how far the tumor has spread. However, CML generally doesn’t lead to tumors — instead, cancer cells travel around the body in the blood. Doctors divide CML cases into phases based on how many leukemia cells are present in the blood.

There are three phases of CML: chronic, accelerated, and blast. Chronic phase CML involves fewer leukemia cells, while blast phase CML involves higher numbers.

How Is the CML Phase Determined?

Cancer specialists have come up with a few different systems to classify CML phases. This means that some doctors may define the phases of CML in slightly different ways. One of the most commonly used systems, described below, comes from the World Health Organization (WHO).

All of these systems are based on the number of blasts (immature white blood cells) in a person’s body. These blast cells may be found in the blood or in the bone marrow (the spongy tissue found inside certain bones), where new blood cells are made.

The systems for determining CML phase may also consider other factors, such as:

  • The levels of other types of blood cells, such as mature white blood cells or platelets
  • Certain symptoms a person has, such as an enlarged spleen
  • Gene changes found within the cancer cells
  • Whether a person’s CML improves after being treated

If you have CML and you notice new or worsening symptoms, talk to your doctor. Make sure to attend all follow-up appointments and tests. This can help you and your doctor keep an eye on your condition and recognize if your leukemia is progressing to a new stage.

Chronic Phase CML

Most people with CML have chronic phase disease. More than 19 out of 20 people with CML are in the chronic phase when they are diagnosed.

Under the WHO system, a person has chronic phase CML if less than 10 percent of the cells in their blood or bone marrow are blasts.

Symptoms of Chronic Phase CML

Some people with chronic phase CML don’t have any symptoms. When symptoms are present, they are usually mild. They may include tiredness, weight loss, abdominal pain, or swelling.

Read more about the symptoms of CML.

Treatments for Chronic Phase CML

Typical CML treatments usually work well for people with chronic phase disease. Blood cell counts will usually return to normal with treatment, and any symptoms will disappear.

Chronic phase CML is usually treated with a type of targeted therapy called tyrosine kinase inhibitors (TKIs). Medications in this category include:

After a person with CML begins treatment, doctors will perform blood and bone marrow tests every three to six months to make sure the TKIs are working. If one TKI isn’t effective, doctors may recommend increasing the dose or trying a different TKI. Doctors may also switch a person’s medications if the first one causes severe side effects.

TKIs generally work well to keep chronic phase CML under control. However, if a person can’t use these medications, or if multiple TKIs are ineffective, there are other options. A person may be able to use chemotherapy or interferon treatments.

Younger people with CML may also be able to get a stem cell transplant. In this procedure, a person’s stem cells (which make new blood cells) are destroyed and replaced with stem cells from a donor.

If chronic phase CML goes untreated, or if treatments don’t work, the leukemia can transform into a more advanced disease phase. Each year, between 1 percent and 1.5 percent of people with chronic phase CML being treated with TKIs progress to a more advanced stage.

Accelerated Phase CML

In the WHO system, a person has accelerated phase CML if they have any of the following:

  • Between 10 percent and 19 percent blasts in their blood or bone marrow
  • At least 20 percent basophils in their blood (a type of white blood cell that is usually found at low levels in the blood)
  • High levels of white blood cells that don’t decrease following treatment
  • Splenomegaly (an enlarged spleen) that doesn’t improve with treatment
  • Very low or very high platelet counts (less than 100 x 103 per microliter or more than 1,000 x 103 per microliter)
  • Certain gene changes within the cancer cells
  • Cancer cells that linger or develop new gene changes during treatment

Other systems may define the accelerated phase differently. For example, some doctors say that a person has accelerated phase CML if they have 15 percent to 29 percent blasts, or if more than 30 percent of a person’s blood cells are blasts or promyelocytes (another type of immature white blood cell).

Symptoms of Accelerated Phase CML

When CML reaches the accelerated phase, people may experience symptoms such as:

  • Fever
  • Tiredness
  • Loss of appetite
  • Weight loss
  • Splenomegaly, which can lead to feelings of pain or fullness in the left upper part of the abdomen or feeling unusually full after eating a small amount

Treatments for Accelerated Phase CML

Standard treatments may not be as effective for people in the accelerated phase of the disease.

People with CML often begin by being treated with imatinib. If this medication does not work and CML progresses to the accelerated phase, doctors may suggest trying a different TKI that may be more effective. Dasatinib and nilotinib are common treatment options during accelerated phase CML. Doctors may use genetic tests to help determine which TKI is most likely to work.

Doctors may also recommend chemotherapy for accelerated phase CML. Stem cell transplantation may be a good option for people who are younger and who have already tried TKIs.

Blast Phase CML

Blast phase, also called blast crisis, is the most severe phase of CML. The WHO system defines blast phase CML as:

  • More than 20 percent blasts in the blood or bone marrow
  • Large clumps of blasts in the bone marrow
  • Clumps of blasts in other organs outside the bone marrow

Other classification systems define blast phase as 30 percent blasts in the blood or bone marrow.

Symptoms of Blast Phase CML

Symptoms are common in blast phase CML. People often experience:

  • Fever
  • Loss of appetite
  • Weight loss
  • Splenomegaly
  • Bone pain
  • Generally feeling unwell
  • Anemia (low levels of red blood cells), which can cause fatigue, dizziness, shortness of breath, or irregular heartbeats
  • Low platelet levels, which may lead to bleeding problems
  • Low levels of healthy white blood cells, which can cause frequent infections

Treatments for Blast Phase CML

Blast phase disease is harder to treat. When CML reaches this phase, doctors may suggest trying different TKIs, chemotherapy, or a stem cell transplant. TKIs often used in blast phase CML include dasatinib, nilotinib, and bosutinib. If all of these are ineffective, ponatinib is another TKI that may be an option. A person may also be able to enroll in a clinical trial to try a new treatment plan not yet available through their doctor.

Cancer cells in blast phase disease divide rapidly and may act like the cells found in acute myeloid leukemia or acute lymphoblastic leukemia (ALL). Chemotherapy drugs used to treat these other cancers may be an option. These treatments are more likely to work if a person’s CML cells behave like ALL cells.

If symptoms are affecting a person’s quality of life, palliative care may be a good idea. These treatments don’t affect the underlying CML, but they can help a person feel better. For example, radiation therapy can help decrease bone pain or shrink the spleen.

Read more about CML treatment options.

How Does CML Phase Affect Prognosis?

Your outlook depends on several factors, including the phase of your leukemia. People with chronic phase CML generally have a very good prognosis, while accelerated or blast phase disease leads to worse outcomes.

Newer targeted therapies are so effective at keeping chronic phase CML under control that researchers still aren’t sure about the survival rates for people with this condition. Most people who started using these treatments 20 years ago are still alive. One study found that 9 out of 10 people with CML who used imatinib lived at least five years.

However, people who have accelerated or blast phase disease have worse outcomes. For example, one study found that 2 out of 3 people with accelerated phase CML lived for five years or more. Those with blast phase CML live an average of seven to 10 months after being diagnosed.

It is important to know that these survival rates are calculated using large groups of people. Your prognosis may look different depending on many factors. If you are younger than 60, don’t have an enlarged spleen, or don’t have elevated levels of blasts, platelets, basophils, or eosinophils, you may have a higher chance of having a good outcome.

Talk to your doctor if you want to learn more about your personal prognosis, or read more about CML survival rates here.

Talk With Others Who Understand

MyLeukemiaTeam is the social network for people with leukemia and their loved ones. On MyLeukemiaTeam, more than 10,400 members come together to ask questions, give advice, and share their stories with others who understand life with leukemia.

Has the phase of your CML changed since you were diagnosed? Have you talked about the different phases with your doctor? Share your experiences in the comments below, or start a conversation by posting on your Activities page.

All updates must be accompanied by text or a picture.
Richard LoCicero, M.D. has a private practice specializing in hematology and medical oncology at the Longstreet Clinic Cancer Center, in Gainesville, Georgia. Review provided by VeriMed Healthcare Network. Learn more about him here.
Maureen McNulty studied molecular genetics and English at Ohio State University. Learn more about her here.

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