Pacritinib Effectively Reduces Symptoms in Patients With Myelofibrosis, Monocytosis

Researchers recently retrospectively analyzed the clinical outcomes of patients with myelofibrosis (MF) with and without monocytosis who were treated with pacritinib, a JAK2 inhibitor, across two phase III trials (PERSIST-1 and PERSIST-2). They presented their findings at the Society of Hematologic Oncology 2024 Annual Meeting in Houston, Texas.

“While sustained monocytosis is a high-risk feature in patients with myelofibrosis, it is also a core diagnostic component for chronic myelomonocytic leukemia (CMML),” the study authors wrote. “Pacritinib is a JAK2 inhibitor approved for myelofibrosis and has potency in the inhibition of CSF1R and IRAK1, kinases upregulated in CMML. Pacritinib has shown some activity in murine CMML models.”

Monocytosis was present in 35 patients (8%) among 430 total participants. Those patients were compared with the 395 who did not have monocytosis.

At baseline, patients with monocytosis had higher median white blood cell counts (11.8×10⁹/L vs 8.9×10⁹/L) and lower median platelet counts (64×10⁹/L vs 89×10⁹/L) compared to those without monocytosis. The study’s primary outcomes at week 24 included spleen volume response (SVR), Total Symptom Score (TSS), and Patient Global Impression of Change (PGIC).

The results showed that both groups had similar rates of SVR and PGIC, indicating that pacritinib’s efficacy was consistent regardless of the presence of monocytosis. Although the TSS response rate was higher in patients with monocytosis, corresponding to a median 55% reduction in symptom score compared to 35% in those without, this difference was not statistically significant (P=0.103). The rates of serious adverse events and drug discontinuation were also comparable between the two groups.

In conclusion, pacritinib provides clinical benefits in patients with myelofibrosis with monocytosis, particularly in symptom reduction, and its efficacy does not appear to be inferior in higher-risk patients compared to those without monocytosis.

Reference

Padron E, Patnaik M, Wiseman D, et al. A retrospective analysis of pacritinib treatment outcomes in myelofibrosis patients with and without monocytosis. Abstract #MPN-499. Presented at the Society of Hematologic Oncology 2024 Annual Meeting; September 4-7, 2024; Houston, Texas.