Clinical Information

The myeloid/lymphoid neoplasms with eosinophilia and rearrangements of PDGFRA, PDGFRB, FGFR1, JAK2, and FLT3 represent a significantly diverse group of hematologic malignancies. Despite the disparate clinical presentations, which include chronic myeloid neoplasms (chronic myelomonocytic leukemia, chronic myeloproliferative neoplasms, chronic eosinophilic leukemia) versus more acute myeloid and lymphoid neoplasms (acute myeloid leukemia, B- and T-lymphoblastic leukemia/lymphoma and mixed phenotypic acute leukemias), this diagnostic subgroup shares rearrangements involving 5 specific gene regions: PDGFRA, PDGFRB, FGFR1, JAK2 and FLT3.

While conventional chromosome studies may detect many of the rearrangements associated with these gene rearrangements, several are cytogenetically "cryptic," including the most common abnormality involving PDGFRA activation. This one megabase submicroscopic, intrachromosomal deletion results in loss of the CHIC2 gene region with subsequent fusion of neighboring genes FIP1L1 and PDGFRA. In addition to this more common, cryptic deletion, the PDGFRA gene has many translocation partners described (at least 15) that similarly result in PDGFRA upregulation.

The PDGFRB, FGFR1, and JAK2 gene regions similarly have numerous translocation/inversion partners described, at least 50 for PDGFRB, 10 for FGFR1, and 40 for JAK2. Despite the significant heterogeneity in gene partners, the identification of PDGFRA, PDGFRB, FGFR1, and JAK2 rearrangements is critical for disease categorization and potential therapeutic intervention. Both PDGFRA and PDGFRB have the potential for response to targeted tyrosine kinase inhibitor therapies such as imatinib mesylate. Similarly, JAK2 rearrangements have the potential for response to targeted inhibitor therapy. Rearrangements of FGFR1 are typically more aggressive and less responsive to targeted inhibitors.

While not formally included in the World Health Organization categorization of myeloid/lymphoid neoplasms with PDGFRA, PDGFRB, FGFR1, or JAK2 rearrangements, rearrangements of the ABL1 gene other than with the BCR locus, can result in similar clinical phenotypes. Thus, the ABL1 gene region has been included in this fluorescence in situ hybridization panel evaluation to appropriately interrogate this gene region, particularly since these patients may not be identified by conventional karyotype analysis and may significantly benefit from targeted tyrosine kinase therapies.