Long-Term Follow Up Of a Randomized Phase II Study Of The JAK2-Selective Inhibitor Fedratinib (SAR302503) In Patients With Myelofibrosis (MF)

We previously reported that patients with MF enrolled in a randomized Phase II study of fedratinib (SAR302503) (ARD11936; NCT01420770) had clinically meaningful reductions in splenomegaly and improvements in MF-associated constitutional symptoms after 24 weeks of treatment (Haematologica 2013;98:S1113). Here, we report updated efficacy and safety results from this study after 48 weeks of treatment (end of Cycle 12).

Patients with intermediate risk-2 or high-risk MF were randomized to receive once-daily fedratinib at doses of 300 mg, 400 mg, or 500 mg, for consecutive 4-weekly cycles, until disease progression or unacceptable toxicity. Eligible patients were aged ≥18 years, with palpable splenomegaly (5 cm below costal margin), and a platelet count ≥50 × 10⁹/L. The primary measure for this study was percent change in spleen volume from baseline at the end of Cycle 3 (Blood 2012:120;Abstract 2837. Haematologica 2013;98:S1113). Endpoints for the current analysis included spleen response (≥35% reduction in spleen volume from baseline, assessed by a blinded independent central review by MRI), safety, and changes in bone marrow fibrosis (BMF).

A total of 31 patients were randomized and treated: median age 63 years, 52% male, 58% primary MF, 58% high-risk MF, 90% JAK2V617F positive. The median numbers of treatment cycles were 12, 14, and 13 in the 300 mg, 400 mg and 500 mg dose groups, respectively, with median durations of exposure of 48.2, 56.2, and 52.4 weeks. At the cut-off date for this analysis, 21 patients (68%) remained on treatment; the most common reasons for treatment discontinuation were adverse events (AEs) (n=5) and withdrawal of consent (n=2). Overall, 58% (18/31) of patients achieved a spleen response at any time during treatment. The median spleen response duration was >35 weeks at all doses (Table). At Week 48, a spleen response was achieved by 30% (3/10), 80% (8/10), and 45% (5/11) of patients in the 300 mg, 400 mg, and 500 mg groups, respectively. Responses were generally maintained across all treatment groups. From Week 24 to Week 48 two additional patients achieved a spleen response (both in the 400 mg group), while one patient in the 500 mg group did not maintain a response (this patient had a fedratinib dose reduction to 200 mg). Changes in BMF up to Week 48 are being evaluated.

The most common non-hematologic AE was diarrhea, with a Grade 3 rate of 13% (4/31 patients) but no Grade 4 cases were recorded. The rates of diarrhea decreased after the first cycle of treatment; from Cycle 2, the incidence of diarrhea (any grade) did not exceed 16% (5/31) at any cycle, and only one case of diarrhea was reported at Week 48 (end of Cycle 12). Anemia was the most-common hematologic toxicity, with a Grade 3 rate of 58% (18/31); no Grade 4 cases were reported. All Grades thrombocytopenia occurred in 55% (17/31) of patients, Grade 3 in three patients, and Grade 4 in two patients. Discontinuation of treatment due to AEs occurred in five patients over the 48 weeks (300 mg [n=2]; 400 mg [n=2]; 500 mg [n=1]), with two cases reported after Week 24 (dyspnea and leukocytosis [400 mg]; anemia and thrombocytopenia [500 mg]). There were 2 deaths (one in the 300 mg group due to unknown reasons [85 days after fedratinib discontinuation] and one in the 500 mg group due to disease progression [36 days after fedratinib discontinuation]). No cases of leukemic transformation were reported.

This updated analysis of the ARD11936 Phase II trial shows that treatment with fedratinib results in durable reductions in splenomegaly in patients with MF. No additional safety signals were observed with prolonged exposure to fedratinib. This study was sponsored by Sanofi.

Pardanani:Sanofi, Bristol Myers Squibb, PharmaMar and JW Pharma: Clinical trial support Other. Jamieson:J&J, Roche: Research Funding; Sanofi: Membership on an entity’s Board of Directors or advisory committees. Lebedinsky:Sanofi: Employment. Gao:Sanofi: Employment. Talpaz:Novartis, Bristol-Myers Squibb, Ariad, Deciphera: Research Funding; Novartis, Bristol-Myers Squibb, Ariad, Deciphera: Speakers Bureau.