What is CML
Overview of CML, its symptoms and diagnosis
One of four types of leukemia, chronic myelogenous leukemia (also known as chronic myeloid leukemia) or CML is a slowly progressing cancer of the blood and bone marrow. It is characterized by an overproduction of white blood cells which do not mature, ultimately cannot carry out their intended function and crowd out the healthy cells.
CML is distinguished from the other types of leukemia by a genetic abnormality in the white blood cells called the Philadelphia chromosome which promotes the growth of leukemia cells and seems to be present in nearly 90% of CML cases. Named for the city where it was discovered, the Philadelphia chromosome is thought to be acquired after birth and is formed when two chromosomes (9 and 22) switch some of their gene material forming a new chromosome.
It is not fully understood as to what causes this chromosomal abnormality, though it appears that exposure to benzene or very high doses of radiation may be significant risk factors. That said, it is important to note that there has been no evidence linking medical or dental x-rays to an increased risk of developing CML.
The Philadelphia chromosome results when a piece of chromosome #9 switches places with a piece of chromosome #22. The translocation forms an extra-long chromosome #9 and an extra-short chromosome #22, which is the Philadelphia chromosome that contains the abnormal, fused BCR-ABL gene.
In Canada, there are approximately 460 new cases each year, which represents 1 case for every 100,000 people. It is estimated that approximately 5,5000 Canadians (2015) are currently living with this very rare form of leukemia, which usually occurs during or after middle age.
Signs and symptoms
Possible signs of CML include lack of energy, exhaustion, and shortness of breath or dizziness when walking or running. Unexplained weight loss, night sweats, fever, and pain and/or a feeling of fullness below the ribs on the left side may also be signs of CML. In many cases however, patients are asymptomatic and are diagnosed from a routine blood test.
Tests that examine the blood and bone marrow are used to detect and diagnose CML. These include:
- A physical exam and history to check for signs of the disease, such as an enlarged spleen.
- A complete blood count (CBC) to check the number of red blood cells, white blood cells and platelets.
- A cytogenetic analysis in which cells in a sample of blood or bone marrow are examined to look for certain changes in the chromosomes, including the presence of the Philadelphia chromosome.
- A bone marrow aspiration and biopsy in which a bone marrow specimen is removed and analyzed for abnormal cells.
- A chemistry screen (blood test) measures the levels of several parts of the blood and is an indicator of general health, helps identify certain problems and detects effectiveness of treatment for a specific problem.
There are three phases of CML:
- Chronic phase – healthy white blood cells are functioning normally although there is an overproduction of abnormal white cells that are in various stages of maturation. Patients may experience few or no symptoms during this phase which can last anywhere from three months to a few years. Most cases of CML are diagnosed during the chronic phase.
- Accelerated phase – there is an increase in the number of white blood cells and immature cells in the bloodstream which crowd out other functioning cells. The bone marrow loses its ability to function and symptoms begin to appear and worsen.
- Blast phase – more than 30% of the cells in the bloodstream and the bone marrow are immature cells, or so-called blast cells. The disease may be life-threatening in this phase.