Prognosis and survival for chronic myelogenous leukemia
People with chronic myelogenous leukemia (CML) may have questions about their prognosis and survival. Prognosis and survival depend on many factors. Only a doctor familiar with a person’s medical history, type of cancer, stage, characteristics of the cancer, treatments chosen and response to treatment can put all of this information together with survival statistics to arrive at a prognosis.
A prognosis is the doctor’s best estimate of how cancer will affect a person, and how it will respond to treatment. A prognostic factor is an aspect of the cancer or a characteristic of the person that the doctor will consider when making a prognosis. A predictive factor influences how a cancer will respond to a certain treatment. Prognostic and predictive factors are often discussed together and they both play a part in deciding on a treatment plan and a prognosis.
Prognostic and predictive factors for CML
The following are prognostic and predictive factors for CML.
People 60 years of age or older have a less favourable prognosis.
CML that is in the accelerated or blast phase at the time of diagnosis has a less favourable prognosis.
Number of blasts
Having a high number of blast cells (blasts) in the blood or bone marrow at diagnosis is a less favourable prognostic factor.
If the spleen is larger than normal at diagnosis, the prognosis is less favourable.
A very low or very high platelet count at diagnosis is a less favourable prognostic factor.
Number of eosinophils and basophils
Eosinophils and basophils are types of granulocytes (white blood cells) that release chemicals to fight some types of infection and during allergic reactions. Higher numbers of eosinophils and basophils in the blood means a less favourable prognosis.
Chromosome changes, or abnormalities, are a prognostic factor for CML.
The Philadelphia chromosome
The most common chromosomal abnormality in people with CML is the Philadelphia (Ph) chromosome. The Ph chromosome is a translocation, or rearrangement, of chromosomes 9 and 22. This translocation creates the BCR-ABL fusion gene, which leads to the development of CML.
About 95% of adults with CML have leukemia cells with the Ph chromosome. When the Ph chromosome is present, CML is described as Ph-positive, or Ph+, CML. When the Ph chromosome isn’t present, it is described as Ph-negative, or Ph–, CML.
People with Ph+ CML have a more favourable prognosis than those with Ph– CML.
Other chromosome changes
If there are other chromosome changes or several chromosome changes, the CML usually has a shorter chronic phase and a less favourable prognosis.
Anemia (low red blood cell count) at diagnosis is a less favourable prognostic factor.
Leukemia cells in the bone marrow
The prognosis is less favourable if there is a large number of leukemia cells in the bone marrow. Having areas of bone damage from growth of leukemia cells at the time of diagnosis is also a less favourable prognostic factor.
Performance status is the measure of how well you can do ordinary tasks and carry out daily activities. People with a low performance status at the time of diagnosis have a less favourable prognosis. This may be because they have other health concerns that make them less tolerant to treatment.
Level of serum lactate dehydrogenase in the blood
A high level of serum lactate dehydrogenase (LDH) in the blood is a less favourable prognostic factor. Higher levels of LDH may mean that there is tissue damage or there are leukemia cells, or blasts, in the blood.
Response to treatment
Doctors measure how effective the treatment is based on if there is a major cytogenetic response. This means a decrease to 35% or less of the leukemia cells with the Ph chromosome. A major cytogenetic response is a more favourable prognostic factor.
Prognostic scoring systems for CML
Doctors use different prognostic scoring systems for CML, including the Sokal, Hasford and European score (or Euro score) systems. These systems take many of the prognostic factors into account to come up with a score used to help doctors predict a prognosis.
These prognostic scoring systems were developed before CML was treated with targeted therapy drugs (tyrosine kinase inhibitors, TKIs) such as imatinib (Gleevec), dasatinib (Sprycel) and nilotinib (Tasigna). These drugs have changed treatment and improved survival. It is not known yet how or if these systems now apply because they have not been used for those who are being treated with targeted therapy.
Doctors have developed a new scoring system since imatinib has been used as treatment for CML. This new system (the EUTOS Score) uses the percentage of basophils in the blood and the size of the spleen to identity people who are less likely to respond to treatment and survive.
Research at the Canadian Centre for Applied Research in Cancer Control led to a new standard in leukemia testing.
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