Efficacy and Safety of Long-Term Ropeginterferon Alfa-2b Treatment in Patients with Low-Risk and High-Risk Polycythemia Vera (PV)

Introduction:

Patients with “low-risk” (LR) PV are managed conservatively despite higher risk of vascular events and impaired quality of life compared to a population without PV. Acknowledging new evidence (LOW-PV study, Barbui et al 2021), recent treatment guidelines (European LeukemiaNet [ELN] 2021) recommend ropeginterferon alfa-2b (BESREMi®) as a cytoreductive treatment in LR PV patients meeting specific criteria as well as in high-risk (HR) PV patients. Final data from the phase 3 PROUD-PV and CONTINUATION-PV trials (NCT01949805; NCT02218047) demonstrated the long-term efficacy and safety of ropeginterferon alfa-2b compared with hydroxyurea/best available treatment (HU/BAT); here we report results in the ropeginterferon alfa-2b arm by risk stratum.

Methods:

PV patients were randomized 1:1 and received ropeginterferon alfa-2b or HU/BAT for ≥6 years. In the ropeginterferon alfa-2b arm, subgroup analyses were performed post-hoc by risk stratum (LR: age ≤60 years and no history of thrombosis; all others HR). Complete hematologic response (CHemR) and molecular response defined by modified ELN criteria were assessed in the full analysis set for CONTINUATION-PV (N=95); safety analyses included all data regardless of roll-over (N=127).

Results:

CONTINUATION-PV enrolled 46 LR and 49 HR patients in the ropeginterferon alfa-2b arm. At baseline, mean age was 50.7 vs 63.7 years respectively, and median duration since PV diagnosis was 1.9 months vs 1.5 months. HR patients had higher platelet and leukocyte counts at baseline and more frequently presented with clinically significant splenomegaly or PV-related symptoms. Median JAK2V617F allele burden was similar for LR and HR patients (37.0% vs 39.4%), however LR patients were less likely to harbor additional non-driver mutations (11.4% vs 24.4%).

The median 4-weekly ropeginterferon alfa-2b dose was comparable in LR and HR patients throughout the study (in the 6^th year, 499 µg and 489µg respectively) as was the use of an extended 3-4 weekly dose regimen (6^th year: 59.5% vs 65.4%).

LR patients achieved a significantly higher CHemR rate than HR patients during long-term treatment (Month 72: 73.2% vs 38.3% in LR and HR respectively [RR: 2.41; 95% CI: 1.50 to 3.90; p=0.0003]). Higher CHemR among LR patients was confirmed in a sensitivity analysis including discontinued patients (last observation carried forward [LOCF]; 80.4% in LR vs 65.3% in HR patients at Month 72) indicating that in the HR group, more patients discontinued despite CHemR. In general, discontinued patients were older than those who completed the study (mean age 62.8 years vs 55.2 years) but did not have a longer duration of PV or markedly greater symptom burden at baseline.

Importantly, regardless of risk stratum, most patients receiving ropeginterferon alfa-2b did not require any phlebotomy for the entire 6^th year (85.7% of LR patients and 75.0% of HR patients entering the 6^th year [p=0.3]).

LR patients had a higher molecular response rate than HR patients (LOCF at Month 72: 84.4% vs 49.0% respectively, RR: 2.15 [95% CI: 1.37 to 3.37]; p=0.0009) and achieved molecular response more rapidly (median time to first response: 12 months [95% CI: 12 to 18] vs 18 months [95% CI: 12 to 24]; Log-rank test p=0.03). The median JAK2V617F allele burden was 5.6% for LR and 17.9% for HR patients at Month 72 (p<0.0001).

During the entire PROUD-PV/CONTINUATION-PV studies (≥6 years exposure), adverse drug reactions (ADRs) to ropeginterferon alfa-2b led to withdrawal of treatment in 1 (1.8%) LR patient (due to sarcoidosis), and in 13 (18.3%) HR patients (due to thrombocytopenia [n=1], elevated transaminases [n=1], psychiatric disorders [n=2], autoimmune disorders [n=6], hypothyroidism [n=2] and dyspnea/pneumonitis [n=1]). LR patients were also less likely than HR patients to experience ADRS of grade ≥3 severity (5.4% vs 23.9%).

Conclusion:

These results demonstrate the benefit of ropeginterferon alfa-2b therapy in both HR and LR patient populations. LR patients may have a greater potential benefit: higher hematologic and molecular response rates can be safely achieved, and the patients are more likely to remain on long-term treatment. These data provide further evidence for an early treatment start as recently outlined by the updated ELN guidelines.