CML is a type of cancer that starts in the blood forming cells of the bone marrow and invades the blood. Leukemia cells tend to build up over time but many people don’t have symptoms for at least a few years. During that time, the cells can invade other parts of the body, including the spleen. CML can also change into the fast growing acute leukemia. Most cases occur in adults, and it rarely occurs in children.
The American Cancer Society’s most recent estimates show about 5,430 new cases will be diagnosed in 2012. About 610 people will die. CML accounts for about 10-15% of all leukemia. CML is slightly more common in men than woman. Over half the cases are diagnosed in people 65 and older. There has been dramatic progress in treating CML in the last few years and most people are surviving for at least 5 years.
There are few known risk factors for CML and for most cases no cause is found. Being exposed to high doses of radiation is the only known environmental risk factor. The risk of getting CML increases with age. The risk does not seem to be affected by smoking, diet, exposure to chemicals or infections.
Many people do not have symptoms when CML is diagnosed. It may be found when a doctor orders blood tests for a different problem. The symptoms can be vague and non- specific.
Symptoms can include the following:
There has been great progress made in the understanding of how changes in DNA can cause normal bone marrow cells to become leukemia cells. This is better understood in CML. When there is swap of chromosomal material between chromosomes 9 and 22, then chromosome 22 becomes shorter. This abnormal chromosome is known as the Philadelphia chromosome. The Philadelphia chromosome is found in the leukemia cells of almost all CML patients.
In order to diagnose leukemia your doctor will ask you questions about your past health and symptoms. Your doctor will do a physical exam and will look for swollen lymph nodes and check to see if your liver or spleen is larger than normal. Blood tests will be ordered to check to see if your white blood cells are high and your other blood cells levels are low. If you have abnormal blood tests then your doctor may do a bone marrow biopsy. This test will look at the inside of your bone. Imaging such as a CT scan, MRI or ultrasound can find out if other organs such as the lung, liver, spleen, lymph nodes, brain and kidneys have been affected as well.
CML is divided into three phases:
The terminal phase leads to complications that are similar to acute leukemia, including a blood infection (sepsis) and bleeding. Some patients progress directly from the chronic to the blast phase. The median survival for someone after a blast crisis is about 3-6 months but can be up to 12 months with remission.
In the last 10 years new drugs that target specific parts of the cancer cells have become a standard treatment option for many cancers. CML cells contain an oncogene, bcr-abl that is not found in normal cells. This gene makes a protein BCR-ABL which causes the CML cells to grow and reproduce out of control. Drugs that target BCR-ABL are called tyrosine kinase inhibitors. These have become standard treatment for CML. Imatinib (Gleevac) was the first drug to specifically target the BCR-ABL gene and is now standard treatment, sometimes with chemotherapy. A bone marrow transplant (BMT) using donor stem cells (allogeneic) or a stem cell transplant is currently the only proven cure for CML.
If a stem cell transplant is successful then the treatment is curative. If not, survival can then be prolonged with a drug such as imatinib. Imatinib is one of the newer drugs that inhibit the specific tyrosine kinase that results from the BCR-ABL gene. It is a well- tolerated drug and is superior to the other regimens using interferon with or without cytosine arabinoside. There are two newer BCR-ABL inhibitors dasatinib (Sprycel) and nilotinib (Tasigna) that have been approved by the Food and Drug Administration to treat adults with newly diagnosed CML, as well as for chronic phase CML resistant to prior therapy that includes imatinib. Other chemotherapy regimens for BCR-ABL negative patients are busulfan, hydroxyurea, and interferon.
Splenectomy may sometimes be used to reduce abdominal discomfort, lessen thrombocytopenia, when the increased size of the spleen cannot be controlled with chemotherapy or radiation.