Interferon in Polycythemia Vera (PV) Yields Improved Myelofibrosis-Free and Overall Survival

Introduction: Polycythemia vera (PV) progression to myelofibrosis (MF) is associated with significant morbidity and mortality. Recombinant interferon alfa (rIFN-α) is the only disease-modifying treatment shown to reverse marrow fibrosis, but the myelofibrosis-free survival (MFS) and overall survival (OS) benefit associated with rIFN-α treatment is yet to be determined. In our preliminary analysis of 306 PV patients (pts) (Abu-Zeinah et al. ASH 2019), those treated with rIFN-α had a longer MFS and OS compared to those treated with hydroxyurea (HU) or phlebotomy-only (PHL-O). Herein, we present the final analysis comparing MFS and OS of 470 PV pts treated with rIFN-α, HU, or PHL-O.

Methods: This single-center retrospective study at Weill Cornell Medicine (WCM) was approved by the WCM institutional review board. Pts were identified by an automated query of the electronic medical record system for the diagnosis of PV and were included if they met the PVSG criteria (1974-2007), WCM criteria (2008-2016) (Silver et al. Blood 2013), and the WHO 2016 criteria (2016-2020). Post-PV MF (PPVMF) diagnosis was made according to IWG-MRT criteria. Both intention-to-treat (ITT) and on-treatment analyses compared the MFS and OS by treatment group and duration, respectively. In the ITT analysis, pts were grouped to rIFNa or HU according to the first treatment they received for at least one year or to PHL-O if no cytoreductive treatment was given. MFS and OS were estimated using Kaplan-Meier methods and the log-rank test compared survival between treatment arms in ITT analysis. Multivariable analysis of PPVMF risk and mortality was performed using a Cox proportional hazards model.

Results: The 470 PV pts identified had a median age of 54 years (range 20-94) at diagnosis; 229 (49%) were women. The median follow-up was 10 years (range 0-45). The primary treatment was rIFN-a in 94 (20%), HU in 188 (40%), other drugs or combinations in 55 (12%), and PHL-O in 133 (28%). The median age at diagnosis for rIFN-a, HU and PHL-O groups was 49, 58 and 54 years respectively (p <0.001) (Table 1). The median MFS for all pts was 23.8 years and for rIFN-a, HU, and PHL-O groups was 32.5, 22.6, and 20.5 years respectively (p <0.001) (Fig 1A-B). The median OS for all pts was 26.7 years and for rIFN-a, HU, and PHL-O groups was 27.7, 25.9 and 21.3 respectively (p<0.01) (Fig 1C-D). In multivariable analysis including age, sex, CV risk factors and thrombosis history, the rIFN-a group had a lower risk of MF compared to the HU group (HR = 0.42, p =0.008) and the PHL-O group (HR = 0.24, p<0.001). Likewise, the rIFN-a group had a lower risk of death compared to the HU group (HR = 0.33, p=0.01) and the PHL-O group (HR 0.3, p=0.001) independent of age. The HU group had a lower risk of PPVMF compared to PHL-O (HR 0.45, p=0.005) but no OS difference. Analysis of longitudinal bone marrow samples showed significantly less MF 2-3 fibrosis in rIFN-a compared to the HU and PHL-O groups (Figure 2). Time on treatment multivariable analysis showed that rIFN-a reduced PPVMF by 6% and all-cause mortality by 8% per year (HR = 0.94, p <0.001 and HR = 0.92, p<0.001 respectively), independent of age, thrombosis history, CV risk factors, or other treatments. On the other hand, HU was not associated with a risk reduction of either MF or mortality. The discontinuation rate of rIFN-a or HU due to toxicity was similar at 2.2 and 2.8 per 100 patient-years.

Discussion: This is the largest single center study in PV using universal diagnostic criteria showing the MFS and OS advantage with rIFN-a over HU or PHL-O, and its similar rates of toxicity to HU. The evidence suggests that early cytoreductive treatment rather than PHL-O is advantageous. Treatment with PHL-O was associated with a higher risk of MF than either rIFN-a or HU.

Conclusion: Our results support early use of rIFN-a as a safe, disease-modifying treatment of rigorously defined PV to delay and potentially prevent PPVMF, and prolong overall survival of PV pts.