FIP1L1-PDGFRA fusion is a genetic abnormality associated with a rare type of blood cancer called hypereosinophilic syndrome (HES) and chronic eosinophilic leukemia (CEL). This fusion gene results from a rearrangement of chromosomes 4 and 10, leading to the fusion of two genes: FIP1L1 (factor interacting with PAPOLA and CPSF1) on chromosome 4 and PDGFRA (platelet-derived growth factor receptor alpha) on chromosome 10. The fusion protein produced by this genetic abnormality leads to the bone marrow to produce too many eosinophils. The cells also express tyrosine kinase constitutively, leading to the uncontrolled cell growth and development of cancer.

The chromosome rearrangement that leads to the FIP1L1-PDGFRA fusion is somatic. The mutation is acquired during a person’s lifetime and cannot be inherited. Only 0.4% of people with persistently high numbers of eosinophils carry the FIP1L1-PDGFRA gene. It is most common in individuals between 20 and 50 years old.

Detecting FIP1L1-PDGFRA fusion is important for the diagnosis and management of patients with HES or CEL. Individuals with FIP1L1-PDGFRA respond well to a Tyrosine Kinase Inhibitor (TKI) called imatinib.