BackgroundMyeloid/lymphoid neoplasms with fibroblast growth factor receptor 1 rearrangements (MLN-FGFR1) are associated with poor prognosis. They are caused by chromosome 8p11 rearrangements that result in FGFR1 fusion genes and constitutive FGFR1 activation. We report on a phase 2 study, in which there were no concurrent control patients, termed FIGHT-203, in which we evaluated the FGFR1–3 inhibitor, pemigatinib, for the treatment of MLN-FGFR1.MethodsWe assigned eligible patients to receive oral pemigatinib 13.5 mg once daily (2 weeks on followed by 1 week off or continuously). End points included complete response rate (primary) and complete cytogenetic response rate. Responses were assessed locally by investigators per protocol-defined criteria and were retrospectively adjudicated by a central review committee using criteria defined by the committee.ResultsOf 47 treated patients (safety population), 45 had confirmed FGFR1 rearrangement and were analyzed for efficacy; of these patients, 24 (53%) were in the chronic phase of illness; 18 (40%) were in blast phase; and three previously treated patients (7%) exhibited the rearrangement without morphologic bone marrow or extramedullary involvement. The overall complete response rate, as determined by central review, was 74% (31 out of 42); this occurred in 96% (23 out of 24) of patients in chronic phase and 44% (8 out of 18) of patients in blast phase. A complete cytogenetic response was observed in 73% (33 out of 45) of patients overall, consisting of 88% (21 out of 24) of patients in chronic phase, 50% (9 out of 18) of patients in blast phase, and all three patients who had a rearrangement only. The median duration of complete response was not reached (95% confidence interval, 27.9 months to not reached). The most common any-grade treatment-emergent adverse event was hyperphosphatemia (76%); the most common grade-3-and-over event was stomatitis (19%). Pemigatinib discontinuation, interruption, and dose reduction occurred in 5 (11%), 30 (64%), and 28 (60%) patients, respectively.ConclusionsIn our study, pemigatinib manifested near complete efficacy in chronic-phase patients with MLN-FGFR1, while the complete response rate was close to 50% in blast-phase patients. Toxicities were manageable with dose modifications. (Funded by Incyte Corporation; FIGHT-203 ClinicalTrials.gov number, NCT03011372.)
Verstovšek et al. (2025) studied this question.