Chronic myelogenous leukemia, also known as chronic myeloid leukemia, is a very rare type of cancer of the blood cells. Fewer than 5,000 people in the United States are diagnosed with it each year. Chronic myelogenous leukemia is often discovered by accident, such as by the presence of a high white blood cell count in routine bloodwork. Since this is the case, many patients do not present with any symptoms when they are diagnosed. Treatments such as bone marrow transplant and chemotherapy that are used for other forms of leukemia are also used to treat chronic myelogenous leukemia.
As with most cancers, chronic myelogenous leukemia can affect people of any age, though it is most common in older adults. Symptoms are wide-ranging and can include fevers with night sweats, gout, decreased resistance to infection, and a general feeling of illness. Even though these symptoms may indicate the presence of cancer, many patients are diagnosed before feeling symptoms. This is because chronic myelogenous leukemia progresses much more slowly than more acute types of cancer. Diagnosis is not based on the presence of symptoms alone, but rather on the detection of a particular type of chromosome abnormality called the Philadelphia chromosome.
Every cell in the human body contains 23 pairs of numbered chromosomes. Sometimes, a certain piece of the ninth chromosome and one from the 22nd can switch places. The break on the ninth chromosome contains a gene sequence known as ABL, while the piece of the 22nd has a gene called BCR. Together, they form the ABL-BCR gene, which instructs a cell to make the protein that eventually leads to chronic myelogenous leukemia.
This error in genetic coding affects the stem cells in bone marrow that are responsible for making blood cells of all types. This form of leukemia is characterized by too many of these stem cells turning into a type of white blood cell called a granulocyte. Not only are there too many of these cells, but they are abnormal and unhealthy. The accumulation of them crowds out healthy cells from the blood, including red blood cells.
There are three phases of chronic myelogenous leukemia, the first being the chronic phase. The vast majority of patients are in this phase when the cancer is detected. In this phase, symptoms are generally mild or nonexistent, but without successful treatment, the cancer progresses to the accelerated phase. This second phase is defined by the presence of certain factors in the blood, or by additional mutations of chromosomes besides the one that began the cancer. The accelerated phase will generally progress to the blast crisis phase, which presents like acute leukemia, and indicates a short time frame for survival. Overall, however, the survival rate is relatively high for this type of cancer, with nearly 90% of patients living five years after diagnosis.