FDA Approval Insights: Pacritinib in Myelofibrosis

Welcome to OncLive On Air^®! I’m your host today, Caroline Seymour.

OncLive On Air^® is a podcast from OncLive^®, which provides oncology professionals with the resources and information they need to provide the best patient care. In both digital and print formats, OncLive^® covers every angle of oncology practice, from new technology to treatment advances to important regulatory decisions.

In today’s episode, sponsored by CTI BioPharma, we had the pleasure of speaking with Ruben A. Mesa, MD, executive director of Mays Cancer Center at UT Health San Antonio, to discuss the FDA approval of pacritinib (Vonjo) in myelofibrosis.

On February 28, 2022, the FDA granted an accelerated approval to pacritinib for the treatment of adult patients with intermediate or high-risk primary or secondary (post-polycythemia vera or post-essential thrombocythemia) myelofibrosis with a platelet count below 50 × 10⁹/L.

The regulatory decision was based on findings from the phase 3 PERSIST-1 (NCT01773187) and PERSIST-2 (NCT02055781) trials, as well as data from the phase 2 PAC203 trial (NCT04884191).

Patients enrolled to the PERSIST-2 trial received pacritinib at a twice-daily dose of 200 mg, and 29% experienced a reduction in spleen volume of at least 30% vs 3% of those who were given best available therapy (BAT), which included ruxolitinib (Jakafi). Moreover, 23% of patients experienced a reduction in total symptom scores of at least 50% vs 13% of those given BAT.

PERSIST-1 enrolled 327 patients with primary myelofibrosis, post-polycythemia vera myelofibrosis, or post-essential thrombocythemia myelofibrosis. These patients were randomized 2:1 to receive pacritinib at a dose of 400 mg daily or physician’s choice of BAT, which excluded ruxolitinib. The trial did not require a specific platelet count for enrollment; however, 32% of patients had levels that were under 100,000 μL, while 16% had levels under 50,000 μL.

PERSIST-2 enrolled 311 patients with myelofibrosis who had platelet counts of 100,000 μL or less. Those in the intent-to-treat population were randomized 1:1:1 to pacritinib at a once-daily dose of 400 mg (n = 75) or a twice-daily dose of 200 mg (n = 74), or BAT (n = 72). Forty-eight percent (n = 149) of participants received prior ruxolitinib.

In PAC203, investigators evaluated the safety and efficacy of pacritinib in patients with primary myelofibrosis who had received prior ruxolitinib. Participants received the agent once daily at 100 mg, twice daily at 100 mg, or twice daily at 200 mg.

Regarding safety, 31% of patients who received the once-daily dose of pacritinib experienced grade 3 or 4 thrombocytopenia vs 32% of those who received the twice-daily dose, and 18% of those who received BAT. Grade 3 or 4 anemia was experienced by 27%, 22%, and 14%, of patients, respectively.

As part of the accelerated approval, CTI BioPharma is expected to provide confirmatory findings of pacritinib in the phase 3 PACIFICA trial (NCT03165734), which is expected to have results by mid-2025.

During our exclusive interview, Mesa discussed the data that led to the regulatory decision with pacritinib, toxicities clinicians should be aware of when prescribing the JAK inhibitor, and the next steps for pacritinib in the space.

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