FIP1L1, 4q12, Green
CHIC2, 4q12, Red
PDGFRA, 4q12, Green
The FIP1L1/CHIC2/PDGFRA product consists of a 177kb probe, labelled in green, located centromeric to the FIP1L1 gene, including the D4S1036 marker, a 174kb probe, labelled in red covering the CHIC2 gene and a 174kb probe, labelled in green, located telomeric to the PDGFRA gene, including the D4S956 marker.
Deletion of CHIC2 (cysteine rich hydrophobic domain 2) at 4q12 results in the fusion of FIP1L1 (factor interacting with PAPOLA and CPSF1) at 4q12 with PDGFRA (platelet derived growth factor receptor alpha) at 4q12 producing a tyrosine kinase which transforms haematopoietic cells1.
In the 2008 World Health Organization (WHO) classification of myeloid neoplasms and acute leukaemia, a new subgroup of myeloid neoplasms was introduced: Myeloid and Lymphoid Neoplasms with Eosinophilia and Abnormalities of PDGFRA, PDGFRB or FGFR1. These neoplasms constitute three specific disease groups, with some shared features1.
The most common myeloproliferative neoplasms (MPN) showing PDGFRA rearrangements are those with FIP1L1-PDGFRA fusions. These MPNs present as chronic eosinophilic leukaemia (CEL) or, more rarely, as acute myeloid leukaemia (AML). As this abnormality is cytogenetically cryptic, FISH provides a useful tool for the detection of the fusion1,2.
Patients with the fusion benefit from treatment with tyrosine kinase inhibitors (TKIs). The diagnosis of the fusion gene can therefore lead to therapeutic choices for the patient1,2.
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