Chronic myeloid leukemia (CML) is a chronic form of leukemia. It is also known as chronic myeloid leukemia. CML occurs when an abnormal gene allows cancer to spread in your body.
Researchers have discovered many chromosome mutations that can cause various types of cancer. There is particularly strong research linking chromosomal mutations and different types of leukemia.
This article examines the relationship between CML and chromosomal mutations.
CML is a type of leukemia that starts in certain cells in your blood marrow called myeloid cells.
Your myeloid cells make red blood cells, platelets, and various types of white blood cells. When you have CML, a genetic change creates an abnormal gene known as BCR-ABL. The BCR-ABL gene causes myeloid cells to spiral out of control. The myeloid cells build up in your bone marrow and eventually spread through your bloodstream.
Leukemia is classified as chronic or acute, depending on how quickly it grows and spreads. CML is a slowly growing, chronic leukemia.
The cancer cells that CML creates usually partially mature. Because these cells are able to act like healthy white blood cells, it often takes years for any symptoms to develop.
Over time, CML can turn into rapidly growing leukemia. At this stage, CML can be difficult to treat.
According to the National Cancer Institute, the 5-year relative survival rate for CML is 70.6 percent. An important factor affecting survival is the stage the CML is in at the time of diagnosis. As with most cancers, early diagnosis makes it easier to treat CML.
There are three phases of CML:
- Chronic phase. The chronic phase of CML can last for several years. At this stage, less than 10 percent of blood and bone marrow cells are cancer cells. Without treatment, the chronic phase can turn into a more aggressive phase.
- Accelerated phase. In the accelerated phase of CML, around 10 to 19 percent of blood and bone cells are cancer cells.
- Explosion phase. This phase is sometimes referred to as the Explosive Crisis. It happens when more than 20 percent of the blood and bone marrow cells are cancerous blasts. People at this stage often have symptoms such as weight loss, fatigue, fever, and an enlarged spleen. CML can be difficult to control at this stage.
Your chromosomes are long molecules of DNA in every cell in your body. Your DNA contains your genes and tells your cells how to function.
Your DNA was given to you by your parents. Because of this, physical traits and some health problems run into families. However, the genes in your DNA can change over the course of your life. This is because your body is making billions of new cells every day, and DNA is copied every time a new cell is made.
Every time a cell divides into two new cells, it has to make a new copy of the DNA in its chromosomes. Most of the time it works the way it’s supposed to. But sometimes errors (mutations) can occur in the genes of DNA when it is replicated for a new cell.
Cancer has been linked to mutations that either:
- Activate genes called oncogenes that accelerate cell growth and division
- Turn off tumor suppressor genes that slow cell division
When cells in certain parts of your body are given the wrong directions and grow and divide much faster than they should, it can cause cancer.
The abnormal chromosomes that cause CML have been studied and well understood by researchers.
We know that CML begins during the process of cell division. Each time a cell divides, 23 pairs of chromosomes have to be copied. CML often starts when part of chromosome 9 goes on chromosome 22 and part of chromosome 22 goes on chromosome 9.
This makes chromosome 22 shorter than normal and chromosome 9 longer than it should be. The shorter chromosome 22 is called the Philadelphia chromosome. About 90 percent of people with CML have the Philadelphia chromosome in their cancer cells.
About the Philadelphia chromosome and the BCR-ABL gene
The exchange of DNA and the formation of the Philadelphia chromosome lead to the formation of a new gene in the body. When the genes on short chromosome 22 and the genes on long chromosome 9 combine, the cancer-promoting BCR-ABL gene (an oncogene) is created.
The BCR-ABL gene carries instructions that tell blood cells to make too much of a protein called tyrosine kinase. This protein enables too many white blood cells to form and circulate. These cells can grow and divide uncontrollably and overwhelm your other blood cells.
Very rarely, CML occurs in cases where there is no Philadelphia chromosome or no BCR-ABL gene. In these cases, there may be undetected mutations that lead to CML.
There are no other known causes of CML. However, there are some risk factors associated with CML. These include:
- Age. The risk of CML increases with age.
- Sex. Men are slightly more likely to develop CML than women.
- Radiation exposure. Exposure to high levels of radiation, for example near a reactor accident, has been linked to an increased risk of CML.
It is possible to have CML for years without any symptoms. Symptoms that occur are easy to confuse with other diseases. This usually includes:
- weakness
- unwanted weight loss
- Loss of appetite
- Feeling of fullness after eating just a small amount
- easy bleeding
- Night sweats
- fatigue
- Bone pain
- a feeling of pain or fullness in the stomach
- an enlarged spleen that you can feel under the left side of your rib cage
If you have symptoms such as accidental weight loss, easy bleeding, night sweats, or an enlarged spleen, see a doctor as soon as possible. While these symptoms can be caused by other medical conditions, it’s always best to get them checked out sooner rather than later.
It’s also a good idea to see a doctor if you have any of the other symptoms of CML, especially if those symptoms persist and don’t seem to be resolved by self-care or lifestyle measures.
Many cancers are linked to changes in the genes that control how cells grow and divide.
Researchers have found a clear link between a particular chromosome mutation and CML. This occurs when parts of chromosome 22 and chromosome 9 are swapped during normal cell division.
When this happens, what is known as the Philadelphia chromosome is created, which is found in around 90 percent of people with CML. The Philadelphia chromosome creates the BCR-ABL gene, which enables white blood cells to divide and grow faster than they should, which can overwhelm your other blood cells.
Make sure to see a doctor if you have a family history of CML or have concerns about this type of cancer.
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