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Home Cancer Leukemia Chronic Myeloid Leukemia (CML)

Chronic Myeloid Leukemia (CML)

Chronic Myeloid Leukemia (CML) affects the myeloid cells in the blood, that is all the blood cells except the lymphocytes. The word chronic describes the comparatively sluggish progress of the disease if left untreated. It has no bearing on the seriousness or the potential ability to cure the disease. Most patients with chronic myeloid leukemia can be treated effectively with anti–cancer drugs. It is not, however, generally considered possible to achieve a cure solely by drug treatment. Nearly all patients with chronic myeloid leukemia will have a distinctive abnormal chromosome in most or all of the leukemia cells. This is produced by bits of one chromosome becoming attached to another and is called the Philadelphia chromosome (Ph1 for short). The abnormality develops as part of the disease and has not been inherited and cannot be passed on to the patient’s children.

Tests for the presence of the Ph1 chromosome can be very valuable to determine whether all the leukemia cells have been eradicated from the bone marrow when a patient is being treated. There are several phases of chronic myeloid leukemia. The likely progress of the disease depends on a large number of factors.

Causes and Phases of CML
Like all forms of leukemia its cause largely remains unknown.

People exposed to high levels of radiation, such as survivors of the atomic bombs in Japan and patients who have received radiotherapy, have a slightly greater chance than other people of developing chronic myeloid leukemia some years later.

There is no clear association of CML with any chemicals, drugs or viral infections.

Treatment for Chronic Myeloid Leukemia
For most patients chronic myeloid leukemia is treatable but not curable. The only treatment known to cure chronic myeloid leukemia is a bone marrow transplant from a healthy donor. The majority of patients with chronic myeloid leukemia are not eligible for bone marrow transplants because of their age. In patients over the age of 55 years the risk of a bone marrow transplant is greater than the likely benefit.

In the initial chronic phase of the disease the symptoms can be controlled with injections of a drug called interferon, and, initially, low doses of a drug called Hydroxyurea are given by mouth. The low doses used have few side effects and are usually tolerated.

Remission is a state in which the disease can no longer be detected by laboratory tests. If there is no trace of disease it is called a complete remission, if there is a marked improvement which falls short of a complete remission this is called a partial remission.

Treatment of chronic myeloid leukemia with drugs may achieve a remission. The remission rarely lasts very long in this situation. The presence of leukemia cells can be shown by testing for the distinctive Philadelphia chromosome.

Interferon, given by injection, is now commonly used as part of the standard treatment of chronic myeloid leukemia. Although interferon does not appear to be capable of curing chronic myeloid leukemia it can achieve long–lasting remissions in about a quarter of patients treated with it. Some patients may find the side–effects of interferon, which are similar to a very severe bout of flu, difficult to tolerate. Interferon is used initially along with Hydroxyurea. If the white blood cell count increases when the patient is taking interferon then Hydroxyurea can be added to control the white count.

As long as the white blood count can be kept under control, and the spleen and liver are not enlarged, patients will have few or no symptoms and can lead a fairly normal life. Patients rarely need to be hospitalized during this phase.

Splenectomy or radiation of the spleen is rarely used today.

Treatment in accelerated or blast phase
Accelerated Phase
Once the disease has entered accelerated phase the only treatment which is effective in preventing or delaying onset of the final blast phase is a bone marrow transplant.

In patients for whom a transplant is not an option, treatment in this phase is aimed at control of symptoms (palliative). Most patients will continue to receive hydroxyurea, possibly with the addition of another drug. Some patients may change from hydroxyurea to busulphan or another drug. Anemia or a low platelet count may be treated with transfusions.

Blast Phase
The blast phase is classified as either myeloid or lymphoid. Most cases are of the myeloid type which is, unfortunately, very resistant to any further treatment and the median survival is only a few months. In the 20 to 30% of cases which are of the lymphoid type the outlook is slightly better, although the median survival is still only about six to eight months.

Lymphoid blast crisis often responds to the type of chemotherapy used for Acute Lymphoblastic Leukemia using a drug called Vincristine with steroids. Although this does not lead to long term survival some patients may have a second chronic phase during which they will again feel relatively well.

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