At a glance

Also known as


Why get tested?
To help investigate the cause of hypereosinophilia (HE) or chronic eosinophilic leukemia, conditions with persistent increase in the number of eosinophils, a specific type of white blood cell. If this gene rearrangement is present the person can be treated with a tyrosine kinase inhibitor (TKI) such as imatinib.
When to get tested?

This test would be arranged by a patient’s doctor before making decisions about the best choice of therapy.


Sample required?
A blood sample drawn from a vein in your arm
Test preparation needed?
Confused about genetics?
See our Genetics Information page

What is being tested?

This is a test for an abnormal gene which can occur in some forms of blood cancers i.e. leukaemia or lymphoma, most commonly chronic eosinophilic leukaemia. The gene is formed by the fusion of fragments of two other genes called PDGFRA and FIP1L1. This fusion gene then produces a fusion protein which is made up of parts of both the PDGFRA and FIP1L1 proteins. 

The PDGFRA gene normally codes for a cell membrane receptor protein. To be turned on the PDGFRA receptor normally needs to bind to another protein called a ligand. However the PDGFRA-FIP1L1 fusion protein receptor no longer responds to ligand binding, it is permanently turned on. This results in continuous signalling to the cell nucleus and unregulated stimulation of cell proliferation, particularly of eosinophils, a type of white blood cell.

How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.

The Test

How is it used?

Many leukaemias and lymphomas are caused by genes being broken apart and then rejoined to form new abnormal genes. These are called “gene fusions”. Many different gene fusions have been identified in different types of leukaemia and lymphoma. The fusion of part of the PDGFRA and FIP1L1 genes most commonly causes chronic eosinophilic leukaemia and this is usually responsive to treatment with therapies called tyrosine kinase inhibitors.  

When is it requested?

This test is performed before a doctor recommends a specific therapy for a patient with leukaemia.

What does the test result mean?

Patients with this specific gene fusion are likely to respond to a class of medications called tyrosine kinase inhibitors.

Is there anything else I should know?

A cancer specialist will use many different tests to identify the treatment most likely to help a patient with a cancer of blood cells. This is just one of the tests that would be used.

Sometimes people develop resistance to imatinib even though the tyrosine kinase inhibitor is usually very effective for treating people with the PDGFRA-FIP1L1 fusion gene at low doses. For the rare individuals whose HE is resistant to imatinib, stem cell transplants have reversed the organ dysfunction caused by hypereosinophilia. However, health practitioners have limited experience with this treatment, so it is not used routinely. Chemotherapy has also been used with some success for people with the fusion gene who don't respond to treatment with imatinib. Some individuals with the fusion gene are also treated with corticosteroids to lower their eosinophil count and help control organ damage.

People with PDGFRA-FIP1L1- may also manifest as acute myeloid or lymphoblastic leukemia, though that is rare. PDGRA-FIP1L1 has also been found infrequently in other leukemias and successfully treated with imatinib.

Unlike some other genetic abnormalities, PDGFRA-FIP1L1 related change is very subtle and thus cannot be detected with routine karyotyping, which involves looking at chromosomes under a microscope.

Common Questions

How common is the PDGFRA-FIP1L1 gene fusion?

This gene fusion causes a particular type of blood cancer that is characterised by lots of eosinophils. This is a rare form of blood cancer, occurring in only 3-60 people per million.

If I have the PDGFRA-FIP1L1 fusion gene, should my family members be tested?

No. The chromosome deletion that leads to the PDGFRA-FIP1L1 fusion is what is known as somatic . It is a mutation acquired during a person's lifetime and cannot be inherited.


Last Review Date: January 9, 2023

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