Polycythaemia vera (PV) is a Philadelphia chromosome-negative myeloproliferative neoplasm (MPN) that, in most cases, harbour the Janus kinase 2 gene (JAK2) driver mutation JAK2V617F [1]. PV is characterised by an over-production of blood cells with increased haematocrit levels, which is a risk factor for thrombotic events (TEs) and cardiovascular mortality [1, 2]. Low-dose aspirin and phlebotomy are usually recommended for patients with low-risk PV (i.e., no history of thrombosis and age ≤60 years). The National Comprehensive Cancer Network (NCCN) recommends ropeginterferon alfa-2b (BESREMi®) as a preferred cytoreductive treatment for patients with low- or high-risk PV [3].

Ropeginterferon alfa-2b is a novel polyethylene glycol (PEG)-conjugated recombinant proline-interferon alpha (IFN-a) with a favourable in vivo pharmacokinetic (PK) profile [4, 5]. Ropeginterferon alfa-2b has demonstrated substantial anti-PV clinical activity, including complete haematologic response (CHR; defined as a haematocrit <45% without phlebotomy, a platelet count ≤ 400 × 10⁹/L, and a white blood cell count ≤10 × 10⁹/L) and a reduction in the JAK2V617F allele burden [6,7,8,9]. Ropeginterferon alfa-2b injection is approved for adult patients with PV at an initial dose of 100 µg (or 50 µg for patients already receiving cytoreductive therapy) with 50 µg incremental intrapatient increases in the dose up to a maximum recommended dose of 500 µg every two weeks. It can take several months to reach the plateau dose level [6]. An alternative dosing regimen with a higher starting dose of 250 µg and simpler intrapatient dose escalation to 500 µg every two weeks with flexible dose adjustment according to tolerability was explored as a treatment option. This regimen controlled PV effectively, as defined by the CHR, and was associated with a shorter time to achieve a CHR [8, 9]. In this report, we aimed to examine the data from the approved slow-dose titration and exploratory higher starting dose regimens focusing on the dynamics of haemoglobin (Hgb) and the occurrence of anaemia. Anaemia is important in the context of PV treatment for several reasons. First, patients who undergo frequent phlebotomy may suffer from symptomatic iron deficiency, leading to anaemia [10]. Anaemia and symptoms can negatively affect the patient well-being and should be avoided in patients with PV and MPNs. The symptoms include headache, insomnia, concentration difficulties, dizziness, restless legs and may coincide and potentiate the disease-related symptoms of the underlying MPN [11,12,13]. Commonly used agents in the PV treatment cause anaemia in substantial numbers of cases ranging from 18% with hydroxyurea (HU) [14] to 72% with ruxolitinib [11, 15]. Anaemia is symptomatic in many cases and may limit the treatment dose or lead to treatment interruption if uncontrolled or severe cases are present. Association between venous thromboembolism and iron-deficiency anaemia has also been shown [16]. Thus, having an agent that can effectively control the elevated haematocrit without excessively suppressing the normal erythropoiesis is a major therapeutic advantage.

An important question regarding ropeginterferon alfa-2b in this context is whether the control of haematocrit is commonly accompanied by clinically significant anaemia, i.e., at the ≥grade 3 level or at the moderate, grade 2 level, but the anaemia is persistent and unmanageable. We therefore performed a retrospective analysis of the effect of ropeginterferon alfa-2b on Hgb levels at various time points or on the occurrence of anaemia with the data available from our two prospective clinical studies in patients with PV.

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