Results of the Myeloproliferative Neoplasms - Research Consortium (MPN-RC) 112 Randomized Trial of Pegylated Interferon Alfa-2a (PEG) Versus Hydroxyurea (HU) Therapy for the Treatment of High Risk Polycythemia Vera (PV) and High Risk Essential Thrombocythemia (ET)

Introduction

HU is the treatment of choice for patients (pts) with high risk ET/PV, however, PEG has been proposed as an alternative option due to its proposed potential to modify disease course. An interim analysis of MPN-RC 112 (Blood 2016 128:479;) did not reveal a difference in PR/CR rates between HU and PEG therapy after 12 months in the first evaluable 75 pts treated. Here we present the results and long-term follow-up of all pts participating in this pivotal study [NCT01259856].

Methods

MPN-RC 112 was a randomized, open label, phase 3 clinical trial comparing HU and PEG in pts with high risk ET/PV. Pts were treated for up to 12 months to achieve PR or CR (ELN/IWG-MRT response criteria). Pts who achieved a PR/CR continued therapy for up to a maximum of 6 years. Minimum follow up was 1 year from the time the last pt was randomized. The primary objective was to compare the CR rate following HU vs. PEG at 12 months with 3 month confirmation. Secondary objectives included a comparison of toxicity and tolerability; PR rates; incidence of specific pre-defined toxicities and tolerance to therapy; impact of therapy on key biomarkers; survival and incidence of myelodysplastic syndrome, myelofibrosis, or leukemic transformation; and incidence of major cardiovascular events. Bone marrow pathologic responses were evaluated by central blinded expert review at baseline, 12, 24 months and end of study.

Results

The study accrued 168 pts; 86 were randomized to HU and 82 to PEG. A summary of pt baseline characteristics by treatment arm is shown in Table 1 and were well balanced between the treatment arms except for median age which was higher in the HU arm (p=0.02). Median duration of follow up was 89.9 weeks (range, 0 to 292.3) and the median treatment duration was 86.0 weeks (range, 0 to 287.3). At 12 months, the overall response rate (ORR= PR+CR) was 69.8% and 78% for HU and PEG, respectively (p=0.22). Figure 1 shows the distribution of responses stratified by disease type. At 24 months, 59 pts were on treatment with an ORR of 22/25 (88%) for HU and 31/34 (91%) for PEG. When considering all 106 pts who were eligible to receive treatment for 24 months (due to study closure), the ORR was 22/54 (40.7%, PR: 11 (20.4%), CR: 11 (20.4%)) for HU and 31/52 (59.6%, (PR: 15 (28.9%), CR: 16 (30.8%)) for PEG, p=0.04. Best ORR at any time on study was seen in 70.9% and 81.7% of HU and PEG treated pts, respectively, p=0.10. The median maximum change from baseline spleen volume was -6% (-100.0 - +53.8) in 112 evaluable pts and was similar between arms, p=0.99.

Bone marrow morphologic responses are shown in Table 2 and the best response (CR) seen at any time on study for ET treated with HU was 52% (12/23) vs PEG 32% (8/25) and for PV treated with HU 19% (6/31) vs PEG 6% (2/34). Cytogenetic analyses at diagnosis were available in 86% (144/168). An abnormal karyotype was seen in 15% (22/144). Five PV and one ET pt lost their chromosomal abnormalities: 3 after one year (HU=1, PEG=2) and three after two years of therapy (HU=2, PEG=1).

AE information is available for 162 pts (HU: 80; PEG: 82) (Table 3). Six pts randomized to HU never received treatment due to study withdrawal prior to initiation of treatment. Sixty pts had a grade 3 or higher event [HU: 22 (27.5%) and PEG: 38 (46.3%)]. 28 PV pts had a grade 3/4 [HU: 10 (24.4%) and PEG: 18 (41.9%)]. Four pts had a grade 4/5 event [HU: 3 (7.3%) and PEG: 1 (2.3%)]. 32 ET pts had a grade 3/4 [HU:12 (30.8%) and PEG:20 (51.3%)]. Two pts had a grade 4/5 event [HU:1 (2.6%), PEG:1 (2.6%)]. Additional outcomes of interest on study include one death attributed to new diagnosis of lung cancer (HU:1), progression to myelofibrosis (HU:1), vertebral artery occlusion (HU:1), and cerebral vascular accident (PEG:1). Reasons for study discontinuation are shown in Table 4.

The effect of therapy on symptom burden and quality of life will be presented in a companion abstract (Mesa et al). The impact of mutation status on therapeutic outcome as well as the molecular responses will be presented at the meeting.

Conclusion

The final analysis of MPN-RC 112 revealed that the CR rates in pts with high risk ET/PV treated with PEG and HU at 12 and 24 months were similar. PEG was associated with a higher rate of grade 3/4 toxicity. Each drug appeared equally capable of modifying the natural history of high risk ET/PV based upon their effects on spleen size, karyotypic abnormalities, histopathological parameters and the low incidence of thrombotic complications and disease evolution in both arms.

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