Prognosis and survival for chronic myeloid leukemia
People with chronic myeloid 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
The following are prognostic and predictive factors for CML.
Taking medicine correctly
CML is treated with tyrosine kinase inhibitors (TKIs). Taking these medicines as prescribed is called compliance. When TKIs are taken correctly, CML has a favourable prognosis.
Age
People who are older than 60 years of age have a less favourable prognosis than people younger than 60.
Phase
CML that is in the accelerated or blast phase at the time of diagnosis has a less favourable prognosis than CML that is diagnosed in the chronic phase.
The Philadelphia chromosome
The genetic change that causes CML is called the BCR-ABL gene. This gene mutation happens when the ABL gene breaks away from chromosome 9 and attaches to the BCR gene on chromosome 22. When chromosome 22 has this mutation, it is called the Philadelphia (Ph) chromosome.
The Ph chromosome is present in everyone with CML, but in rare cases it can't be found during testing. When it is found, the disease is described as Ph-positive (Ph+) CML. If the Ph chromosome can't be found, it is called Ph-negative (Ph–) CML.
Ph+ CML has a more favourable prognosis than Ph– CML.
Additional chromosome abnormalities
Additional chromosome abnormalities (ACA) are genetic changes other than the BCR-ABL gene that causes CML. These abnormalities increase the risk that CML will progress from one phase to another. They also increase the risk that CML won't respond to, or will stop responding to, treatment.
Enlarged spleen
With CML, granulocytes with the BCR-ABL gene (called leukemia cells or CML cells) can collect in the spleen. As a result, the spleen can swell and get bigger.
If the spleen is larger than normal at diagnosis, the prognosis is less favourable. The larger the spleen is, the less favourable the prognosis.
Platelet count
Having a very low or a very high platelet count at diagnosis is a less favourable prognostic factor.
Prognostic scoring systems for CML
Doctors use different scoring systems to help them determine a prognosis and estimate survival for CML. These systems use many of the same prognostic factors, but they use different calculations or formulas to determine their scores. Talk to your healthcare team about which prognostic score they will use to predict your response to treatment and your prognosis.
The European Treatment and Outcome Study (EUTOS) score is based on the percentage of basophils (a type of granulocyte) in the blood and the size of the spleen. It can be used to predict how likely it is that someone will have a complete cytogenetic response after treatment with a tyrosine kinase inhibitor (TKI) such as imatinib (Gleevec). This score also helps predict the likelihood that the person with CML will live at least 5 years without the disease getting worse (called 5-year progression-free survival).
- A l ow-risk score means there is a 90% chance of 5-year progression-free survival.
- A high-risk score means there is an 82% chance of 5-year progression-free survival.
The EUTOS long-term survival (ELTS) score can be used to predict how well a person will respond to treatment with imatinib, how likely they are to have a complete cytogenetic response and how long they will survive. It measures the risk of dying from CML within 10 years. Its formula uses age, spleen size, percentage of granulocytes with the BCR-ABL gene (leukemia cells or CML cells) in the blood and platelet count.
- A low-risk score means there is a 2% risk of a CML-related death in 10 years.
- An intermediate-risk score means there is a 15% risk of a CML-related death in 10 years.
- A high-risk score means there is a 40% risk of a CML-related death in 10 years.