A Phase II Trial of Pegylated Interferon α-2b in Polycythemia Vera and Essential Thrombocythemia. Clinical Responses, Effects on PRV-1 Expression and Impact on Quality of Life.

Background α-interferon (IFN) is an effective treatment in polycythemia vera (PV) and essential thrombocythemia (ET). IFN can induce cytogenetic remissions in PV pts. However, 21–25 % of pts discontinue therapy due to side effects. Pegylated IFN has been suggested to have less side effects.

Study design and patients: The Nordic MPD Study Group performed an open label phase II feasibility study of PegIntron® treatment in 42 MPD pts, 20 females and 22 males, median age 54 yr (range 29–77). Inclusion criteria were a platelet count of > 400x10⁹/L in pts with symptoms or previous thrombosis (n=26) or >1000x10⁹/L in asymptomatic pts without previous thrombosis (n=16). 22 pts had PV, 20 ET. 15 pts had previously received cytoreductive therapy; anagrelide (7), hydroxyurea (6), busulfan (1), P32 (1). Previous IFN therapy was not allowed. Median time from diagnosis to study start was 0.74 ys (0.01–30.2). Initial dose was 0.5 μg/kg once weekly. The treatment goal was a platelet count < 400x10⁹/L in symptomatic patients and < 600 in asymptomatic patients (CR). If CR was not achieved within 12 weeks PegIntron was increased to 1 μg/kg/week. The dose was subsequently decreased to the lowest dose maintaining CR. Pts QoL was investigated using QLQ-C30 and HAD forms. Neutrophil PRV-1 mRNA expression was analyzed by quantitative RT-PCR prior to and after therapy.

Results: Response to treatment was evaluated at 1,2,3,6,9 and 12 months. At 6 months, 29/42 pts (69 %) had achieved CR, after a median time of 83 days. The median dose at time of CR was 0.5 μg/kg/week. CR rate was not related to diagnosis or gender. 4/42 pts (10%) discontinued therapy early due to side effects, another 9 pts were taken off study at 6 months due to side effects or insufficient response. Only 4/14 responding PV pts required phlebotomy therapy, compared to 20/22 before PegIntron. 20/29 patients with CR at 6 months maintained CR at 12 months, whereas 9 pts had gone off study due to side effects. The mean platelet count was 875x10⁹/L prior to therapy, and 512, 448, 362x10⁹/L at 3,6 and 12 months in pts on therapy. No thrombotic or bleeding complications were observed. Side effects were common, the majority WHO grades I-II; fatigue (76 %), injection site reaction (64 %), flu-like symptoms (64 %), headache (56 %), muscle pain (51 %), depression (35 %), insomnia (24 %), hair loss (20 %). Mild elevations were noted of serum ALAT, creatinine and TSH in 19, 3 and 3 pts respectively. QoL data will be presented. Changes in PRV-1 expression were determined in 13 PRV-1 positive pts (9 PV, 4 ET) after 6 months and in 2 PV pts after 24 months. PRV-1 expression was normalized in 3/4 ET pts at 6 months and in 1/2 PV pts after 24 months treatment.

Conclusion: We found PegIntron to be effective in reducing the platelet count in 29/42 pts (69 %) and 20 pts (48 %) remained in CR at 1 year. 22 pts (52 %) had discontinued therapy at 12 months, mainly due to side effects, a higher rate than in previous trials. Although analyzed in a small number of pts, reversal of PRV-1 positivity nonetheless suggests that PRV-1 quantification may be useful as a molecular marker of therapeutic efficacy.