Chronic myelogenous leukemia (or chronic myeloid leukemia, abbreviated CML), is a kind of cancer that occurs in a specialized white blood cell called a myelocyte. In the bone marrow, where all blood cells are made, immature myelocytes acquire a genetic abnormality, cease to function normally, and multiply in uncontrolled fashion. This is known as "malignant" change - that is, cancer of the myelocytes. CML is slow to develop and may affect a person for many years.
When the malignant cells grow in the bone marrow, normal bloods cells are often destroyed or crowded out. Having fewer normal white cells can cause the person to become infected easily. The infections may be serious and life-threatening. Having fewer platelets means that the person may bruise or bleed easily. Anemia, or low numbers of red blood cells, can make the person weak and easily tired.
CML cells eventually leave the bone marrow and travel throughout the body in the bloodstream. So many CML cells may enter the bloodstream that the blood becomes too thick. The number of CML cells may be up to 150 times the normal number. However, these CML cells do not function like normal myelocytes.
Many times, CML causes no symptoms and is found only when a routine blood sample is checked. The most common symptom is severe fatigue. The person may also have unexplained weight loss and night sweats. Occasionally, the person can feel pain in the upper left side of the abdomen due to a swollen spleen.
In most cases, the cause of CML is unknown. Some cases have been linked to exposure to high-dose radiation (such as the atomic bomb blasts in Japan) or to inherited abnormalities.
There is no known way to prevent CML.
Diagnosis of CML begins with a medical history and physical exam. A blood sample is examined to look for abnormal cells. Genetic studies may be done on the blood sample as well. This helps to identify any special characteristics of the leukemia. A sample of bone marrow will be removed and examined by a pathologist. This procedure is known as a bone marrow biopsy.
The early part of the disease, when it is causing few problems, is called the chronic phase. Eventually, CML cells will begin multiplying very rapidly. At that time, the disease will be similar to acute nonlymphocytic leukemia (ANLL). CML is said to be in terminal phase (or "blast crisis") because there are so many immature white cells in the body. At that point the disease is difficult to treat and may lead to death. This may happen several months or years after the disease is diagnosed.
CML is not contagious and poses no risk to others.
Chemotherapy with medicines such as hydroxyurea (i.e., Hydrea) or busulfan (i.e., Myleran) may decrease the numbers of CML cells for many years. Interferon, a natural substance produced by white cells, may also help the body control the CML cells. Known as a biological response modifier, interferon does not cure the cancer. It can only control it for a period of time.
Some people are given the bone marrow from another person to help recovery. This is called a bone marrow transplant. A bone marrow transplant during this phase may cure the person. This therapy is very intense and may not be right for every person who has CML.
During the terminal phase, CML will be treated like acute leukemia. High doses of chemotherapy may be given intravenously. If the cancerous cells can be destroyed, a stage known as remission, the person may be considered for a bone marrow transplant. Remission is usually followed by additional therapy.
Chemotherapy given during the chronic phase causes only mild side effects. Mild nausea will usually pass with time. The medicines given during the terminal phase cause many side effects. Interferon can cause long-term flu-like symptoms.
Bone marrow transplantation is a very high-risk procedure undertaken only when near-certain death is the alternative. The individual will be in a facility that specializes in bone marrow transplants, and will be at risk for life-threatening infections and other complications for several weeks until his new immune system takes hold. With intensive care, most of these side effects are managed successfully and many patients do well long term.
The person with CML will need to be followed closely for signs of the disease worsening. Persons who have had a bone marrow transplant will need lifelong follow-up even if the disease is in remission.
During the chronic phase, blood samples will be monitored closely for signs that the CML is not under control. When this happens, a bone marrow biopsy will be done. The same follow-up strategy is used for a patient who is in remission after therapy. Any new or worsening symptoms should be reported to the healthcare provider.
Khouri, I, Sanchez, F.G., Deisseroth, A.(1997). Leukemias in Cancer: Principles and Practice of Oncology. 5th Edition DeVita, V.T. (ed). J.B. Lippincott: Philadelphia. Pp. 2287-2321.