Complete Hematological, Molecular and Histological Remissions without Cytoreductive Treatment Lasting After Pegylated-Interferon α-2a (peg-IFNα-2a) Therapy in Polycythemia Vera (PV): Long Term Results of a Phase 2 Trial

Two phase 2 studies have recently shown promising results of peg-IFNα-2a therapy in PV and essential thrombocythemia, including major efficacy, satisfactory tolerance, and significant molecular responses, renewing the interest for IFNα therapy in patients (pts) with MPN. However, no prospective study has assessed the long-term safety and efficacy of IFN therapy in those pts. We analyzed the long-term results of the PVN1 trial (www.clinicaltrials.gov #NCT00241241), a phase 2 study of peg-IFNα-2a therapy in PV, after a median follow-up (FU) of 6.4 years.

40 PV pts were enrolled in the study between Sept 04 and Sept 05. 4 pts were not evaluable (1 inclusion criteria violation, 2 withdraws of consent, 1 allergic reaction at first injection). Median age was 50 yrs (range 22–65). Median time since diagnosis was 6 months (range 1–65). 9 pts (25%) had previously received hydroxyurea. 6 pts (17%) had a history of thrombosis. 7 pts (20%) had splenomegaly. Long-term analyses were performed in 34 patients in June 11 (2 pts lost to FU). Hematological, molecular and histological responses were assessed according to the European LeukemiaNet (ELN) criteria.

Median FU was 77.4 months (mos) (Q1−Q3: 72 – 81 mos) and median duration of peg-IFNα-2a therapy was 47.4 mos (Q1-Q3: 28 – 77 mos). Clinical-hematological efficacy: At last evaluation, 32/34 pts (94%) were in hematological response including 28/34 complete responses (CR) (82%) and 4 partial responses (PR), and 2 pts had relapsed. 14 pts (41%) were still treated with peg-IFNα-2a for a median time of 70 mos. During FU, 20 pts stopped IFN after having received the drug for a median time of 42 mos. Among them, 10 pts (29% of the total cohort) had stopped because of sustained hematological CR, 8 (23%) because of toxicity, and 2 (6%) at investigator's discretion. 13 (38% of the total cohort) of the 20 pts who stopped therapy did not received any other cytoreductive treatment after peg-IFNα-2a discontinuation, and 10/13 were still in hematological CR off-therapy at last evaluation after a mean observation period of 28+ mos (range 3+ – 64+ mos). During FU, PV relapsed in 3/13 pts who had stopped cytoreductive therapy after a mean time of 25 mos (range 6 – 37 mos). Peg-IFNα-2a was restarted in 2 of them and a second hematological CR was achieved. None of the patients experienced any vascular event during FU, when about 10 events would have been expected in this series of 34 PV pts followed for 77 mos (5.5% pts/year in the ECLAP study). Molecular and histological responses: Molecular response was assessed by measuring JAK2V617F allele burden in granulocytes (%V617F) in 29 pts with serial samples: a molecular response was achieved in 24 pts (83%) including 8 molecular CR (28%), and only 5 pts (17%) had no decrease in their %V617F. Mean %V617F was 47% (range 10 – 100%) at baseline, and 10% (range 0 – 45%) at 72 mos. 4 pts had a TET2 mutation: in none of them the TET2 mutant allele burden decreased during therapy although median decrease in %V617F in the same samples was 100% (Q1 – Q3: 75% – 100%). Bone marrow biopsies performed in some pts in hematological CR after discontinuation of peg-IFNα-2a found a normalized BM morphology fulfilling the ELN criteria for histological CR, and excluded an evolution to myelofibrosis as a cause for “apparent” remission. Toxicity: Peg-IFNα-2a was stopped because of adverse event in 8 pts (23%): fatigue in 2, depression in 1, grade 2 neuropathy in 1, arthralgia in 1, thyroiditis in 1, auto-antibodies in 1, liver enzyme elevation in 1 pt, respectively. Importantly, no unexpected adverse event was observed in spite of the very long-term use of peg-IFNα-2a (median of 45.5 mos).

In this prospective phase 2 study of PV pts treated with peg-IFNα-2a after 6.4 years median FU, we recognized that: 1) 94% of pts were still in hematological response, including 82% CR; 2) 29% of pts could stop peg-IFNα-2a and remained in hematological response without further cytoreductive therapy after a median observation time of 28+ mos (up to 64+ mos); 3) major and sustained molecular response in %V617F was confirmed in 83% of patients, including 28% who achieved complete molecular response, while TET2 mutated clones appeared resistant to peg-IFNα-2a; 4) histological CR was also achieved in selected patients; 5) no vascular event was observed after 6.4 years median FU; 6) no new safety concern arose with prolonged utilization of peg-IFN alpha-2a.

Off Label Use: Phase 2 study of pegylated-Interferon alpha-2a in polycythemia vera (off-label).