Effect Of Treatment With The JAK2-Selective Inhibitor Fedratinib (SAR302503) On Bone Marrow Histology In Patients With Myeloproliferative Neoplasms With Myelofibrosis

Fedratinib, a JAK2-selective inhibitor, demonstrated clinical benefit through a reduction in splenomegaly and symptoms in patients with myelofibrosis (MF), including post-polycythemia vera MF (post-PV MF), post-essential thrombocythemia MF (post-ET MF) and primary MF (PMF), in Phase I and II studies (J Clin Oncol 2011;29:789; Haematologica 2013;98:S1113). Bone marrow fibrosis (BMF) has been associated with splenomegaly and cytopenias (Ann Hematol 2006;85:226). Hence, stabilization and/or reversal of BMF remain important therapeutic goals. This report represents an exploratory analysis of sequential BMF data from patients with MF in an open-label Phase I/II study to evaluate the long-term effects of orally administered fedratinib (TED12015; NCT00724334).

Patients with intermediate or high-risk MF (Mayo Prognostic Scoring System) received fedratinib therapy in consecutive cycles (1 cycle = 28 days) as long as they derived clinical benefit. Bone marrow trephine biopsies were performed at baseline and after every 6 cycles. Hematoxylin and eosin, reticulin, and Masson's trichrome staining of core biopsy slides were used to grade BMF on a scale from 0 to 3 using the 2008 WHO MF grading criteria. BMF was graded independently in a blinded fashion by 3 hematopathologists. BMF grades were established as long as at least 2 of the 3 pathologists agreed independently. Changes in BMF grade from baseline were categorized as improvement (≥1 grade reduction), stabilization (no change), or worsening (≥1 grade increase).

Of the 43 patients enrolled in the TED12015 study, the median fedratinib dose received was 473 (range 144–683) mg/day and median treatment duration was 32.3 (range 7–61) cycles. Bone marrow biopsies at baseline and at least one other time point were available for 21/43 (49%) patients, whose baseline characteristics were: median age 61 years (range 43–85); 57% male; 38% high-risk MF by WHO 2008 criteria (Leukemia 2008; 22:14); and 90% JAK2V617F positive. A consensus grade was achieved for 96% of the samples. At baseline, 2, 10, and 9 patients had grade 1, 2, and 3 BMF, respectively. Changes in BMF grade from baseline are shown in the figure. BMF improvement with 1 grade reduction was observed in 8/18 (44%) patients at Cycle 6. By Cycle 30, 4/9 (44%) evaluable patients had BMF improvement, including 2 patients with improvement by 2 grades and 2 patients with improvement by 1 grade. Of patients with Grade 3 BMF at baseline, 6/9 (67%) exhibited 1 grade improvement at Cycle 6. Two patients had 2 grades of BMF reduction from baseline during treatment (grade 3 to 1, and grade 2 to 0, both at Cycle 12), and the latter achieved a complete clinical remission at Cycle 30 assessed by IWG-MRT response criteria. The two patients who experienced complete reversal of BMF to grade 0 (one from grade 2 and one from grade 1) had normalization of not only hemoglobin level but also white blood cell and platelet counts at Cycle 18.

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These exploratory analyses suggest that a proportion of patients treated long-term with fedratinib demonstrate stable or improved BMF. The disease modifying impact of fedratinib on BMF changes will be further assessed in a randomized, placebo-controlled Phase III clinical trial (JAKARTA; NCT01437787). This study was sponsored by Sanofi.

Jamieson:J&J, Roche: Research Funding; Sanofi: Membership on an entity’s Board of Directors or advisory committees. Hasserjian:Sanofi, Inc: Consultancy. Gotlib:Sanofi: Travel to EHA 2012, Travel to EHA 2012 Other; Sanofi: Membership on an entity’s Board of Directors or advisory committees; Sanofi: Research Funding. Cortes:Incyte, Sanofi: Consultancy; Incyte, Sanofi: Research Funding. Talpaz:Novartis, Bristol-Myers Squibb, Ariad, Deciphera: Research Funding; Novartis, Bristol-Myers Squibb, Ariad, Deciphera: Speakers Bureau. Thiele:AOP Orphan Pharmaceuticals, Incyte, Novartis, Shire, Sanofi: Consultancy; Novartis, Shire: Research Funding; AOP Orphan Pharmaceuticals, Incyte, Novartis, Shire, Sanofi: Honoraria. Rodig:Ventana/Roche Inc.: Research Funding; Daiichi-Sankyo/Arqule Inc., Ventana/Roche Inc., Shape Pharmaceuticals Inc.: Consultancy. Patki:Sanofi: Employment. Wu:Sanofi: Employment. Wu:Sanofi: Employment. Pozdnyakova:Sanofi: Honoraria; Sanofi: Consultancy.