Efficacy and Safety of Pegylated Interferon Alpha-2a in Patients with Essential Thrombocythemia and Polycythemia Vera: Results after a Median 7-Year Follow-up of a Phase 2 Study
Authors: Masarova Lucia , Verstovsek Srdan , Patel Keyur P. , Newberry Kate J , Cortes Jorge E. , Borthakur Gautam , Konopleva Marina , Estrov Zeev , Kantarjian Hagop M. 
Published: October 2019

Abstract
Introduction: It has been previously reported that pegylated interferon alpha-2a can induce hematologic and molecular responses in patients with essential thrombocythemia "ET" and polycythemia vera "PV", but the follow up in these studies were relatively short.
Objective: We present longer-term efficacy and safety results of a prospective phase II study of pegylated interferon alpha-2a in patients with ET and PV after a median follow up of 82.5 months (range, 8-107).
Methods: Patients with a diagnosis of ET or PV, in a need of therapy, either newly diagnosed or previously treated, were eligible for this study. Median interferon starting dose of 180 mcg/week SQ (range, 450-90; 39% started on 90mcg/week) was modified in majority of the patients based on toxicity or lack of efficacy. Clinical and molecular responses were assessed every 3 to 6 months.
Results: Among 83 enrolled patients (43 PV, 40 ET), 32 patients (39%) are still on study (but in 8 therapy is on hold: 5 due to toxicity, and 3 for financial reasons). Median age was 53 years (range, 19-78). Overall 37% of patients did not receive prior cytoreductive treatment. The overall median exposure to therapy was 87 months (range, 58-107) and was no different for patients still enrolled on the study and those who stopped study participation. Nine (28%) patients still on study are currently on a dose equal or higher than 90 mcg/week and 15 (47%) are on dose equal or smaller than 45mcg/week. JAK2 status or allele burden had no impact on achievement of response (clinical or molecular), time to response or duration of therapy. 55 of 59 (71%) JAK2V617F positive patients were evaluable for molecular response (Figure); 8 patients carried CARL mutation, 3 carried MPL and in 13 were triple negative. Median duration of hematologic and molecular response was 66 and 53 months, respectively; and directly correlated with treatment length and type of response (CMR had the longest duration of response). Overall yearly discontinuation rate were gradually decreasing for first 5 years, from 17% to 5%, and slowly increasing afterward to 10%. Of the 51 patients not on the study anymore, 27 (35% of the total) discontinued therapy primarily due to treatment toxicity. New late (≥24 months from start of therapy) G3/4 toxicity occurred in 17% of patients. Among patients in complete hematologic response treatment failure due to vascular adverse event or disease transformation was seen in 5 patients each. Three patients died on study (not related to therapy or disease), and 8 after stopping participation. Mean changes in allele burden over time in JAK2 positive patients are depicted in figure.
Conclusions: Although pegylated interferon alpha-2a can induce significant hematologic and molecular responses; toxicity still limits its use over longer period of time and loss of response or transformation is encountered. Table.ResponseCharacteristicsFirst responseLast responseHem Resp, N. of patients (No), (%)CHR62 (76)25 (40)aPHR4 (5)1 (25)ORR66 (79)26 (39)aMol Resp, No, (%)CMR10 (18)9 (90)PMR20 (36)5 (25)*mMR5 (9)2 (40)ORR35 (74)16 (46)SafetyAny gradeGrade≥3Overall Adverse Events (AE), No, (%)any AE83 (100)57 (67)recurrent AE74 (89)13 (16)AE subtypes, No, (%)musculoskeletal73 (88)6 (8)neurological53 (64)2 (4)psychiatric38 (46)4 (11)gastrointestinal54 (65)11 (20)LFT elevation27 (33)5 (18)skin18 (22)2 (11)infection/fever26 (31)3 (12)respiratory23 (28)2 (9)cardiovascular13 (16)3 (23)metabolic16 (19)2 (13)neutropenia37 (45)21 (57)thrombocytopenia18 (22)a1 (6)anemia36 (43)1 (3)Autoimmune toxicity, No, (%)hepatitis1 (2.5)CNS vasculitis1 (2.5)lupus nephritis1 (2.3)Sjogren sy & dermatitis1 (2.5)Vascular AE (TEE/bleeding),Unprovoked6 (7)5 (83)No, (%)Provoked4 (5)3 (75)Disease transformation, No, (%)Myelofibrosis6 (7)AML1 (1)Safety over ≥24 months**Any gradeGrade≥3New AE, No (%)3th year10 (17)4 (40)4th year6 (11)4 (67)5th year5 (10)1 (20)≥ 6th year10 (24)1 (10)**Effective sample size for patients on therapy/year: Initial number of patients at risk at the beginning of period minus half of patients censored during that period*% calculated from 19 patientsastatistically significant differences by Fisher's exact testAbbr. CMR= complete molecular remission (undetectable JAK2 allele burden), PMR= partial molecular remission (>50% decrease in allele burden), mMR= minor molecular remission (20-49% decrease in allele burden)
Figure 1. Figure 1.

Disclosures
Off Label Use: Pegylated Interferon alfa-2a used for patients with essential thrombocythemia and polycythemia vera. Cortes:Novartis: Consultancy, Research Funding; BerGenBio AS: Research Funding; Teva: Research Funding; BMS: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; Ariad: Consultancy, Research Funding; Astellas: Consultancy, Research Funding; Ambit: Consultancy, Research Funding; Arog: Research Funding; Celator: Research Funding; Jenssen: Consultancy. Konopleva:Novartis: Research Funding; AbbVie: Research Funding; Stemline: Research Funding; Calithera: Research Funding; Threshold: Research Funding.