Pacritinib was significantly more effective than the best available treatment (BAT) at reducing spleen volume and symptom burden in patients with myelofibrosis (MF) and severe thrombocytopenia, according to a retrospective analysis of data from two phase III clinical trials.
The analysis, led by Srdan Verstovsek, MD, PhD, of the University of Texas MD Anderson Cancer Center, was published in Haematologica.
The retrospective analysis of efficacy and safety data included 189 patients with MF and severe thrombocytopenia who received pacritinib (n = 132) or BAT (n = 57) in the PERSIST-1 and PERSIST-2 clinical trials. The median age of patients was 69 years (range, 50-91 years). Most patients (72%) had primary MF. The median time since diagnosis was two years.
The most common therapies used in patients receiving BAT were no active treatment (37%; with 25% receiving no active treatment for the entire trial), ruxolitinib (30%), hydroxyurea (28%), and prednisone (12%).
The analysis endpoints included the percentage of patients reaching a spleen volume reduction of ≥35% (SVR35), the percentage of patients achieving a total symptom score reduction of ≥50% (TSS50), and the percentage of patients who reported that their symptoms were “much” or “very much” improved. All endpoints were assessed at week 24.
A significantly greater percentage of patients treated with pacritinib met efficacy endpoints for SVR35 (23%) compared to patients receiving BAT (2%; P=.0007). Higher response rates were reported in patients treated with a twice-daily dose of pacritinib 200 mg (29%) compared to patients treated with a once-daily dose of pacritinib 400 mg (20.5%). Pacritinib-treated patients had a significantly greater median percentage reduction (−29.4%) in spleen volume than patients receiving BAT (−1.3%; P<.0001).
A significantly higher proportion of pacritinib-treated patients achieved TSS50 (25%) compared to patients receiving BAT (8%; P=.044). A significantly higher percentage of the pacritinib-treated group self-reported “much” or “very much” improved symptoms (25%) compared to patients receiving BAT (8%; P=.016).
The adverse event profile of pacritinib was manageable, and dose modification was rarely required, with no excess in bleeding or death reported in pacritinib-treated patients, the study reported.
The retrospective analysis results “highlight the important role that pacritinib may play in the future therapeutic landscape for patients living with cytopenic MF,” the authors wrote.
The randomized, phase III PACIFICA trial is currently underway comparing a twice-daily dose of pacritinib 200 mg to physicians’ choice of therapy in patients with MF and severe thrombocytopenia. The trial findings “should confirm whether pacritinib will be a new therapeutic option for patients with cytopenic MF,” according to Dr. Verstovsek and colleagues.