The Effect of JAK 1/2 Inhibitors on Outcomes of Allogeneic Stem Cell Transplantation for Patients with Myelofibrosis

Abstract Introduction: Ruxolitinib was the first JAK 1/2 inhibitor (JAKi) approved for myelofibrosis (MF), with several other JAKi in development. Ruxolitinib was approved on the basis of reducing splenomegaly and improving constitutional symptoms, but its effect on subsequent allogeneic stem cell transplantation (SCT) is not well understood. Retrospective studies to date have reported mixed outcomes after SCT for MF patients with previous exposure to JAKi. In this multicenter retrospective study, we report on outcomes of patients with MF treated with SCT at our institutions. Methods: We analyzed outcomes for 184 consecutive patients at three institutions who underwent SCT for primary or secondary MF. Primary outcomes included overall survival (OS), progression free survival (PFS), and graft-versus-host-disease (GVHD)-free and relapse-free survival (GRFS), all measured from the time of SCT. Cox proportional hazard regressions were fit to estimate the association between the use of JAK 1/2 inhibitors prior to SCT and OS, PFS, and GRFS, adjusting for donor type and DIPSS-plus status. p Results: 72 patients received a JAKi prior to SCT, while 112 did not. Patients in these two groups were well-matched with respect to age, sex, DIPSS plus score, conditioning, and donor type (Table 1). Median follow-up was 31.2 months (range: 0.8-146.3 months). In univariate analysis, there was no difference in OS (JAKi: 4-yr OS 56.7% [95% CI 40.9-69.8%] vs. no JAKi: 43.6% [95% CI 32.9-53.9%], p=0.49), PFS (JAKi: 4 yr PFS 54.1% [95% CI 40.8-65.7%] vs. no JAKi: 43.9% [95% CI 33.4-53.9%], p=0.77), or GRFS (JAKi: 8-month GRFS 56.6% [95% CI 44.1-67.4%] vs. no JAKi: 50.4% [95% CI 40.4-59.5%], p=0.62) in the overall population; there was similarly no difference when comparing only intermediate-risk or only high-risk patients. In multivariate analysis, there was no difference in these outcomes for patients based on previous JAKi exposure when accounting for DIPSS plus score and donor type (related vs unrelated). Rates of acute GVHD were similar between the two groups (JAKi: 53.5% vs. no JAKi: 55.0%, p=0.88), including grade 3 or 4 acute GVHD (JAKi: 16.9% vs no JAKi: 19.8%, p=0.70). Conclusions: Our data suggest that there is no statistically significant difference in OS, PFS, GRFS, or rates of acute GVHD after SCT for MF patients based on previous JAKi treatment. This was true overall and after adjusting for DIPSS plus risk score or donor type. Given the retrospective design of our study, we were not able to assess prior response to JAKi or splenomegaly at SCT, which may influence outcomes. Given mixed results in the literature to date, we eagerly await the results of ongoing phase 2 trials of JAKi prior to SCT for MF. Disclosures Ho: Jazz Pharmaceuticals: Consultancy. Fathi: Astellas: Honoraria; Jazz: Honoraria; Boston Biomedical: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Agios: Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Seattle Genetics: Consultancy, Honoraria. Chen: Takeda Pharmaceuticals: Consultancy; Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees; Magenta Therapeutics: Consultancy; REGiMMUNE: Consultancy. Hoffman: Formation Biologics: Research Funding; Incyte: Research Funding; Janssen: Research Funding; Merus: Research Funding; Summer Road: Research Funding. Mascarenhas: Novartis: Research Funding; Merck: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees, Research Funding; Promedior: Research Funding; Janssen: Research Funding; Roche: Research Funding; CTI Biopharma: Membership on an entity's Board of Directors or advisory committees, Research Funding.