Pacritinib Therapy Shows Improved Symptom Reduction and Spleen Response for Patients With Myelofibrosis and Thrombocytopenia
Key Clinical Summary
- Population and Design: Multicenter retrospective chart review of 169 patients with primary or secondary MF treated with pacritinib between June 2022 to July 2024; 61.5% first-line, 38.5% second-line (93.8% post-ruxolitinib); median age 71 years, 91.1% with thrombocytopenia (median PLT 45×10⁹/L), and median follow-up 9.2 months.
- Efficacy: At Day 180, 45.6% showed spleen size improvement (84.2% among those with severe baseline splenomegaly); platelet count increased 37.5%, with 38% achieving IWG platelet response; median hemoglobin + 0.5 g/dL, and 34.3% of anemic patients improved ≥ 1 g/dL.
- Symptom and Survival Outcomes: 82.7% of symptomatic patients reported reduced symptom burden (median 67% decrease in total symptoms); Day 180 survival probability 93.5% (95% CI, 88.6 to 96.3), consistent across treatment lines.
- Clinical Relevance: Pacritinib demonstrated clinically meaningful improvements in spleen volume, cytopenias, and symptom burden, with durable responses and favorable tolerability across both first-line and ruxolitinib-exposed MF patients, supporting its role as an effective therapy regardless of baseline thrombocytopenia.
Pacritinib (PAC) demonstrated significant clinical benefit, including spleen size reduction, improved hematologic parameters, and decreased symptom burden, regardless of treatment line or baseline thrombocytopenia among patients with intermediate- or high-risk myelofibrosis (MF), according to real-world study results published in Blood.
Previous research has found pacritinib, a JAK1-sparing JAK2/IRAK1/ACVR1 inhibitor, to be efficacious for patients with MF and severe thrombocytopenia, resulting in reduced spleen volume and symptom improvement. However, research on real-world treatment patterns and patient outcomes with pacritinib remain limited.
To address this need, researchers conducted a real-world, multicenter retrospective chart review of 169 patients with primary or secondary MF who initiated pacritinib between June 2022 and July 2024 across predominantly community settings. Eligible patients were treated in either the first line (1L, 61.5%) or second line (2L, 38.5%) setting, with 93.8% of second line patients previously treated with ruxolitinib.
Most patients had thrombocytopenia (91.1%; platelet [PLT] <100 × 10⁹/L), and the median platelet count at pacritinib initiation was 45 × 10⁹/L. Median age at diagnosis was 71 years (interquartile range [IQR], 65.0 to 76.0), and 52% of patients were male. After a median follow-up of 9.2 months [IQR, 6.8 to 13.2), 73.4% of patients remained on pacritinib therapy. At baseline, the median platelet count was 45.0x109/L (IQR: 40.0-50.0) and most patients (91.1%) presented with thrombocytopenia (platelet <100x109/L), with 26.8% having a platelet count greater than 50x109/L. The median hemoglobin was 9.0 g/dL (IQ, 8.1 to 9.8) and most patients had hemoglobin <10 g/dL (77.3%).
Among 68 patients with evaluable spleen measurements at baseline and Day 180, 45.6% experienced improvement in spleen size category. Spleen reductions were most pronounced in patients with severe splenomegaly at baseline, 84.2% of whom had improvement in spleen size.
By Day 180, platelet count increased by a median of 37.5%, with 38% achieving a platelet response per IWG criteria, defined as absolute increase of ≥30,000/µL during index treatment among those with a pre-index platelet count less than 20 to 100. Median hemoglobin improved by 0.5 g/dL, and 34.3% of patients with baseline hemoglobin <10 g/dL had a ≥1.0 g/dL improvement.
Most patients (96%) reported MF-related symptoms at baseline, with fatigue being the most common (84%). By Day 180, 82.7% of symptomatic patients experienced a reduction in symptom burden, with a median 67% reduction in total number of symptoms.The survival probability at Day 180 from pacritinib initiation was 93.5% (95% confidence interval [CI], 88.6 to 96.3). Results were consistent in both first line and second line JAK inhibitor-treated patients.
The researchers concluded, “In real-world clinical settings, [patients] with MF treated with PAC, regardless of the line of therapy, experienced reduction or stabilization in spleen size category, improvement in hematologic parameters, and a diminution of MF symptom burden.”
Source:
Tremblay D, Oladapo A, Marrone M, et al. Real-world treatment patterns and clinical outcomes in patients with myelofibrosis treated with pacritinib (PAC): Results from the my-PAC study. Blood. November 3, 2025. doi:10.1182/blood-2025-4607
