Individualized Dosing of Ropeginterferon Alfa-2b Ensures Optimal Response in Patients with Low-Risk Polycythemia Vera (PV)

Introduction:

Ropeginterferon alfa-2b at a fixed dose of 100 µg/2 weeks was efficacious in patients with low-risk polycythemia vera (PV) in the Low-PV trial, but the response rate was lower in a group of patients who switched to ropeginterferon alfa-2b after failing to respond to phlebotomy alone (Barbui et al., 2023). The finding that this group had a higher proportion of males and higher baseline values for body-mass index, phlebotomy demand, blood counts and JAK2V617F allele burden suggests that these characteristics might predict a higher dose requirement of ropeginterferon alfa-2b. We analyzed low-risk PV patients from the PROUD-PV/CONTINUATION-PV (NCT01949805/NCT02218047) cohort to examine the impact of baseline characteristics and individually optimized dose levels of ropeginterferon alfa-2b on response status at 12, 24 and 72 months.

Methods:

Patients diagnosed with PV (WHO 2008 criteria) were randomized 1:1 and received ropeginterferon alfa-2b or standard care for a total of ≥6 years during the 12-month PROUD-PV study and its extension CONTINUATION-PV. Low-risk patients (aged ≤60 years with no history of thrombosis) allocated to the ropeginterferon alfa-2b arm were analyzed. Ropeginterferon alfa-2b was started at a dose of 100 µg/2 weeks (50 µg if transitioning from hydroxyurea) and escalated by 50 µg/2 weeks until blood counts normalized to a maximum of 500 µg/2 weeks. Grade 2-3 drug-related toxicity mandated dose reduction/interruption. During maintenance treatment the dosing interval could be extended to 3-4 weeks. Complete hematologic response (CHR) defined by modified ELN criteria (without the spleen criterion) and safety data at 12, 24 and 72 months were assessed.

Results:

In the setting of individualized dosing, 33/56 (58.9%) low-risk PV patients allocated to ropeginterferon alfa-2b in PROUD-PV achieved a CHR at month 12. Response rates increased with longer treatment duration; of the 46 low-risk patients enrolled in CONTINUATION-PV; 80.4% and 73.2% of patients with available data achieved a CHR at months 24 and 72, respectively.

Baseline characteristics by response status at month 12 indicated that males were overrepresented among non-responders (15/23 non-responders [65.2%] were male vs 11/33 responders [33.3%] [p=0.0291]), and baseline median JAK2V617F allele burden was non-significantly higher in non-responders at 12 months (45.6% vs 35.5%: p=0.1860). However, no significant differences in these baseline parameters were observed by long-term response status (24 months or 72 months), nor were there consistent differences in baseline body mass index or blood counts according to response status at any time point evaluated.

The most frequent reason for non-response was failure to meet the CHR criterion hematocrit <45% without phlebotomy in the past 3 months, accounting for the majority of non-responders at months 12, 24 and 72 (13/23 [56.5%], 6/9 [66.7%], and 6/11 [54.5%], respectively), followed by discontinuation for any reason, which accounted for 30.4% of non-responders at month 12 and 36.4% at month 72. Only one low-risk patient discontinued due to ropeginterferon alfa-2b-related toxicity.

Despite response-driven dosing, the median 4-weekly derived dose of ropeginterferon alfa-2b in the first year was only somewhat higher in non-responders compared with responders (809 µg [range: 209-898] vs 717 µg [188-898]; p=0.6954); 10/23 of non-responders at month 12 did not escalate the dose immediately according to protocol on ≥1 occasion during the first year, e.g. due to responses already observed for leukocyte or platelet counts. In the second year, the median 4-weekly doses were 997 µg (range: 211-997) vs 690 µg (88-1036) respectively (p=0.2024), indicating that non-responders received and tolerated the maximum dose (500 µg/2 weeks).

Conclusions:

High long-term response rates (80.4% at 24 months; 73.2% at 72 months) were achieved with ropeginterferon alfa-2b treatment in the low-risk PV population when the dose was optimized on an individual basis. No specific baseline characteristics among low-risk PV patients appear to be associated with long-term response to ropeginterferon alfa-2b. However, the PROUD-PV/CONTINUATION-PV studies show that - as hypothesized based on the Low-PV trial data - some low-risk patients require and can tolerate high doses, and that the optimal dose of ropeginterferon alfa-2b varies substantially between patients.