CML: Chronic Myeloid Leukemia
Leukemia is a type of cancer of the blood and the bone marrow (the inner part of bones where blood cells are made). In patients with leukemia, the following things happen.
First, certain types of your blood cells turn into cancer cells. Second, the body keeps producing large numbers of these abnormal cells. CML is one type of leukemia. "Chronic" means that it is a slower-growing cancer that may take years to progress (unlike acute leukemia, which progresses very quickly). "Myeloid" refers to the type of white blood cell being overproduced. So, CML is a slowly progressing cancer that makes the body produce too many cancerous myeloid white blood cells.
There are three phases of CML: the chronic phase, the accelerated phase, and the blast crisis phase. As patients move through these phases, their disease progresses, and they experience more physical symptoms. Most patients find out that they have CML in the early, chronic phase and many will remain in chronic phase for a number of years without progressing to more advanced phases of Ph+ CML.
Why Does It Happen?
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When a person is healthy, signals in the body tell it to produce new blood cells. These signals reach early cells, called stem cells, which mature into various types of blood cells. The signals turn stem cells on and off as necessary to produce the number of blood cells the body needs. When a person has CML, a change takes place in the person's DNA and makes this signal stay on constantly. Since this signal stays on, the body produces more and more abnormal cells.
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How Is It Treated?
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CML can be treated with a bone marrow transplant (BMT), with drug therapy, or with a combination of the two. The decision in favor of transplant versus drug treatment depends on a number of factors and will be made by the patient and treating physician together.
BMT is also known as a stem cell transplant (SCT). This type of therapy involves two steps. First, a very high dose of one or more drugs is given to the patient to kill most of the cells in the bone marrow (cancer cells and healthy cells). The second step is to replace the destroyed stem cells with only healthy cells.
These replacement cells are usually taken from someone else (this is known as an allogeneic transplant). For an allogeneic transplant to succeed, the cells taken must closely match those of the patient. Unfortunately, finding a matched donor—related or unrelated—is often difficult.
Occasionally, replacement cells are taken from the patient (this is known as an autologous transplant). This procedure is generally less complicated than an allogeneic transplant, but the cancer is more likely to return.
Whether a patient receives an allogeneic transplant or an autologous transplant, once the stem cells are replaced, they settle into the patient's bone marrow and start to grow and produce blood cells.
BMT is the only treatment that has been shown to cure some patients with CML, so this is the first treatment that physicians may consider for their patients. Unfortunately, there are many risks with the procedure, and only a fraction of patients are appropriate candidates for it.
The drug most commonly used to treat Ph+ CML is Gleevec®. You will find a wealth of information on what Gleevec does and how to use it throughout this website. If Gleevec is not an option, other drugs may be used to treat Ph+ CML:
Interferon-alpha (IFN-α). Interferons are natural substances produced by the body. Giving patients an injection of IFN-α may help slow the growth of leukemia cells (and prolong life), but it does not provide a cure for CML. IFN-α is sometimes given alone, and sometimes given with the drug cytarabine (ara-C). The most significant problem with this therapy has been with tolerability. Many patients cannot tolerate the side effects of IFN-α therapy.1
Hydroxyurea/busulfan These two oral chemotherapy agents are typically used with patients who are unable to receive a BMT and who do not respond to or cannot tolerate IFN-α . Chemotherapy agents are chemicals (drugs) used to destroy leukemia cells. Both of these therapies treat the symptoms of CML, but they do not prolong life. However, they are generally better tolerated than IFN-α therapy.
1Faderl S, Kantarjian HM, Talpaz M. Chronic myelogenous leukemia: update on biology and treatment. Oncology (Huntingt). 1999;13:169-180,181,184.
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