Chronic myelogenous leukemia (CML) arises when a genetic mutation called the Philadelphia chromosome occurs in the blood cells. This abnormal chromosome forms a protein (called BCR/ABL) that is the hallmark of the disease.
According to the American Cancer Society, approximately 4,570 new cases of CML were diagnosed in the United States in 2010. The average age at diagnosis is 65, and the disease is slightly more common in men than women. Researchers have noticed an increasing proportion of younger people with CML in recent years.
CML develops when genetic material is exchanged between two of the 46 chromosomes that are in human cells. It typically occurs between chromosomes 9 and 22, although in a small percentage of patients additional chromosomes are involved as well.
The Philadelphia chromosome is the name for the abnormal chromosome 22. The scrambled genetic material on chromosome 22, called the BCR/ABL fusion gene, directs the cell to produce a protein that triggers a runaway growth of a type of white blood cell called myeloid cells. Exactly how the BCR/ABL fusion protein does this is not clear.
Patients with CML typically have elevated white blood cell counts and may have low numbers of red blood cells (a condition called anemia) as well as elevated levels of platelets. Cells that contain the Philadelphia chromosome eventually accumulate in large numbers in the bone marrow.
Chronic leukemias often develop gradually, and symptoms may not appear for several years.
Doctors classify CML into three phases (chronic, accelerated, and blastic), which are usually defined by the percentage of immature cells, or blasts, in the bone marrow, as well as other features.
In the first stages of CML, many patients do not have any symptoms of disease and remain symptom-free for several years. Frequently, the disease is discovered through routine blood tests or during a regular checkup. With the passage of time, however, as the number of diseased cells accumulates and interferes with the body’s normal functioning, symptoms develop. These symptoms can include:
- bleeding and bruising
- shortness of breath
- weight loss
- enlarged lymph nodes
- a feeling of fullness in the abdomen
- night sweats
- loss of appetite
- recurrent infections
These symptoms can also be caused by other conditions and do not necessarily mean that you have CML. Speak with your doctor if you have any of these symptoms to ensure proper diagnosis and treatment.
Risk factors for developing CML are poorly understood. Exposure to radiation and some chemicals are known risk factors. Most people with CML have no known risk factors at all.