What Is Chronic Myelogenous Leukemia?
Chronic myelogenous leukemia (CML), also known as chronic myeloid leukemia, is a type of bone marrow cancer in which the bone marrow produces too many mature white blood cells. CML is most often a slowly progressing disease that is chronic (long-term).
People with CML have acquired an abnormality that causes a short chromosome, called the Philadelphia chromosome. This leads to the development of an abnormal gene BCR-ABL, which acts as a switch that is stuck in the “on” position to stimulate a type of white blood cells called granulocytes to grow out of control. These can build up in the blood and bone marrow so there is less room for healthy white blood cells, red blood cells, and platelets. The overgrowth of white blood cells increases the size of the spleen.
CML accounts for 15 percent of all leukemias in adults. About 8,000 new cases are diagnosed each year in the United States. About half of patients diagnosed are 65 years old or older.
Risk factors include:
- Being exposed to high-dose radiation
- Age — the risk of developing CML increases with age
- Being male
Symptoms and Signs
Because CML progresses relatively slowly, people may not have any symptoms in its early stages. Sometimes CML does not cause any symptoms at all.
The most common signs of CML include:
- Unexplained weight or appetite loss
- Weakness or fatigue
- Shortness of breath
- Easy bruising
- Night sweats
- Pain or fullness below the ribs on the left side
Growth and Outlook
CML is classified into phases that help predict a patient's prognosis. The phases are based mainly on the number of immature white blood cells — myeloblasts (or blasts) — that are seen in the blood or bone marrow.
CML: Three Phases
The disease has three general phases: chronic phase, accelerated phase, and blastic phase. Most patients are diagnosed in the chronic phase. As the amount of blast cells increases in the blood and bone marrow, there is less room for healthy white blood cells, red blood cells, and platelets. This may result in infections, anemia, and easy bleeding, as well as bone pain. The number of blast cells in the blood and bone marrow and the severity of signs or symptoms determine the phase of the disease.
- In the chronic phase, fewer than 10 percent of the cells in the blood and bone marrow are blast cells.
- In the accelerated phase, 10 to 19 percent of the cells in the blood and bone marrow are blast cells.
- In the blastic phase, 20 percent or more of the cells in the blood or bone marrow are blast cells. When tiredness, fever, and an enlarged spleen occur during the blastic phase, it is called blast crisis.
Along with the phase, other factors — such as a person's age, spleen size, and/or blood counts — may help predict the outlook and can sometimes inform the treatment plan. We take these factors into account using the Sokal and Hasford prognostic scoring systems.