There are three phases of chronic myeloid leukemia: chronic, accelerated, and blastic. Knowing which phase you're in can help you and your doctor determine your treatment method.

What is chronic myeloid leukemia?

Chronic myeloid leukemia, or CML, is one of four types of cancer that begins in the bone marrow. It starts in the blood-forming cells and can eventually spread throughout the body via the blood. Because CML is a chronic form of cancer, it comes on gradually and lasts for years. This differs from acute types of leukemia, which begin suddenly and are immediately life-threatening.

CML is caused by a genetic mutation that results in blood cells producing too much of the tyrosine kinase protein. This protein causes an overproduction of diseased blood cells, and allows them to live too long. Eventually, these diseased cells leave no room for healthy blood cells.

Phases of CML

There are three phases of CML: chronic, accelerated, and blastic. The phase is determined by the progression of the disease and is measured by the number of blast cells. Blast cells are abnormal white blood cells that don’t mature properly and crowd out healthy cells.


The first phase of CML is the chronic phase. Most people are diagnosed with CML during this phase. During the chronic phase, cancer cells grow and multiply slowly. This phase can last indefinitely and symptoms are very mild or not present at all. Those with CML may not even know they have the disease for several years. A diagnosis usually results from blood tests given for an unrelated reason.


A relatively small number of people will progress from the chronic phase to the accelerated phase. In the accelerated phase, the blast cells grow and multiply more quickly, and they seem to stop responding to treatment. People in this phase may notice symptoms like fatigue, caused by a lower number of red blood cells, and stomach pain due to an enlarged spleen. Other features of this phase include a low platelet count and unusually high or low numbers of white blood cells.


If left untreated, those with CML can progress to the third phase. In the blastic phase, the blast cells have reached a critical level. These levels are sometimes equal to those seen in people with acute leukemia. This surge of blast cells leads to dangerously low levels of red blood cells and platelets. Symptoms are more severe, and can include:

  • rash
  • bruising and bleeding easily
  • bone and joint pain
  • stomach pain
  • more pronounced fatigue
  • difficulty breathing
  • increased risk of infection
  • night sweats
  • weight loss

During the blastic phase, CML is difficult to treat and is considered to be life-threatening.

Treatment options

When diagnosed in the chronic phase, CML is usually first treated with drugs called tyrosine kinase inhibitors, or TKIs. TKIs are medications that target the protein produced by the cancerous cells. This type of treatment is often enough to put CML into remission. In some cases, oral chemotherapy is also used to kill off some white blood cells, if white cell levels have become too high. Though these drugs cannot completely cure CML, people usually respond quite well and remain in remission for many years.

More aggressive treatment options must be considered for those in the accelerated phase. Stem cell transplants or bone marrow transplants are the next course of treatment, and can result in a true cure.

Transplants are also recommended for those who have progressed to the blastic phase. Treatment is much more difficult during this phase because there are fewer healthy cells.

Staying healthy

It’s very important to follow your doctor’s recommended course of treatment when you’re diagnosed with CML. Waiting until you have unpleasant symptoms or until you have reached the accelerated or blastic phase can make your CML much harder to treat.