Identification and Confirmation of Myeloid/Lymphoid Neoplasms With Fibroblast Growth Factor Receptor 1 Rearrangement and Characterization of Treatment Patterns and Outcomes in a Real-World Setting: A US Retrospective Chart Review.

Introduction: Myeloid/lymphoid neoplasms with fibroblast growth factor receptor 1 rearrangement (MLN-FGFR1) are rare, heterogenous, aggressive hematologic malignancies with FGFR1 rearrangements at the 8p11 locus. Pemigatinib, a potent selective inhibitor of FGFR1-3, is approved for relapsed/refractory MLN-FGFR1.

Methods: This retrospective chart review included US adults with myeloproliferative neoplasm, unclassifiable (MPN-U), myelodysplastic syndrome(MDS)/MPN, post-MPN acute myelogenous leukemia, precursor T- or B-cell acute lymphoblastic leukemia/lymphoma, or mixed-phenotype acute leukemia with bone marrow biopsy and standard cytogenetic and/or molecular results. Probable cases of MLN-FGFR1 were identified and confirmed with cytogenetic or molecular testing results. Patient characteristics, diagnostic testing methods, treatments, and outcomes were abstracted.

Results: Of 560 submitted cases, 51 (9.1%) were probable MLN-FGFR1, 33 (5.9%) of which were subsequently confirmed. Among patients with confirmed MLN-FGFR1, 8p11 translocation or FGFR1 rearrangements were detected with standard cytogenetics in 72.7%, break-apart fluorescence in situ hybridization in 66.7%, next-generation sequencing in 21.2%, and real-time polymerase chain reaction in 6.1%. All but 1 patient initiated treatment; 3 patients underwent allogenic stem-cell transplant.

Conclusion: This study highlights the importance of cytogenetic and molecular evaluations in patients with chronic/blast phase hematologic malignancies to diagnose MLN-FGFR1. This is particularly important following US approval of pemigatinib for this hematologic malignancy.