Pacritinib shows symptom and spleen response regardless of cytopenias in patients with MF

Patients diagnosed with myelofibrosis (MF) are commonly administered JAK inhibitor (JAKi) therapy to reduce splenomegaly and improve disease symptoms. However, treatment is limited for patients with cytopenic MF as JAKi’s may exacerbate their condition. Pacritinib is a novel JAK1-sparing inhibitor that is being investigated at full dosage levels in patients regardless of the presence of cytopenias.

During the 2023 American Society of Clinical Oncology (ASCO) Annual Meeting, Bose presented a retrospective analysis investigating the effects of pacritinib on spleen and symptom benefit across the cytopenic spectrum in patients enrolled in the PERSIST-1 (NCT01773187) and PERSIST-2 (NCT02055781) trials. Below, we summarize the key findings.

For more information on the use of pacritinib in patients with cytopenic MF prior to allogeneic-hematopoietic stem cell transplantation, check out our previous article.

Study design

• Patients analyzed were stratified according to baseline blood counts.
  • platelet counts <100 × 10⁹/L
  • platelet counts ≥100 × 10⁹/L
  • hemoglobin <8 g/dL
  • hemoglobin 8 to <10 g/dL
  • hemoglobin ≥10 g/dL
• Analysis endpoints:
  • spleen volume reduction (SVR)
  • median percentage change in SVR over time
  • total symptom score (TSS)
  • percentage change in total symptom score over time
• Patient global impression of change was used to measure the change in patient reported symptoms.

Results

• A total of 276 patients were included in the analysis
• Out of the total cohort, 70% of patients had primary MF
• Only 16% of patients had prior JAKi treatment exposure
• The median dose intensity of 100% was maintained across all patient subgroups
• SVR at Week 24 was experienced consistently by patients across the platelet and hemoglobin stratification.
  • SVR ≥35% in 21–28% of patients
  • SVR ≥25% in 39–44% of patients
  • SVR ≥10% in 75.5–82% of patients
  • SVR of any grade in 84–93% of patients
• SVR by Week 12 was also experienced consistently in both patient subgroups
• Any improvement in TSS was experienced by 80–87% of patients according to platelet and hemoglobin stratification
  • TSS ≥50 was highest in patients with baseline hemoglobin <8 g/dL (62.5%)
• Improvement in TSS was experienced by Week 12 and continued through Week 36
• Based on patient global impression of change, 80% of patients reported an improvement in disease symptoms
• At Week 24, around half of patients reported ‘very much’ or ‘much’ improved symptoms
• The median level of hemoglobin remained consistent through Week 24

Conclusion

Results from this analysis demonstrate efficacy of pacritinib for spleen and symptom response, independent of baseline blood counts. The ongoing and consistent clinical effect observed in patients may be due to pacritinib’s unique mechanism of action, allowing for full dosage regardless of cytopenias.