Pacritinib Spleen Response Yielded OS Benefit in Cytopenic Myelofibrosis

By Leah Lawrence - Last Updated: September 18, 2023

Spleen volume reduction (SVR) was associated with a significant overall survival (OS) benefit among patients with myelofibrosis with low platelets treated with the JAK2/IRAK1/ACVR1 inhibitor pacritinib, according to data presented at the Eleventh Annual Meeting of the Society of Hematologic Oncology in Houston, Texas.

Helen Ajufo, MD, of Memorial Sloan Kettering Cancer Center, presented retrospective results from a landmark OS analysis of the PERSIST-2 study from patients with myelofibrosis who had platelets ≤100×109/L.

In PERSIST-2, treatment with pacritinib demonstrated a significant SVR benefit compared with the best available therapy, including ruxolitinib. Although SVR is used as a surrogate endpoint for disease response in, it is not known whether SVR is associated with a survival benefit in patients with low platelet counts.

This analysis included patients at the start of the 12-week SVR window who received pacritinib 200 mg twice daily or the best available therapy. An SVR of 10% or more was associated with a significant OS benefit when treated with pacritinib. The threshold of 10% demonstrated the greatest separation in the OS curves between responders and nonresponders. At this threshold, no deaths occurred in responders compared with five deaths in nonresponders (P<.0001).

The researchers acknowledged that an SVR of 35% of more is a standard response threshold but added that it was a less predictive indicator of survival on pacritinib, as many patients with SVR less than 35% were long-term survivors.

Achieving SVR on best available therapy in this patient group was not associated with improved survival, regardless of the SVR threshold used.

“As pacritinib can be given at full dose regardless of platelet count, it may offer a unique survival advantage for [myelofibrosis] patients with moderate or severe thrombocytopenia who achieve spleen reduction,” they concluded.


Ajufo H, Bewersdorf JP, Harrison C, et al. SVR (Spleen Volume Reduction) Predicts OS (Overall Survival) in MF (Myelofibrosis) Patients on PAC (Pacritinib) but Not BAT (Best Available Therapy): PERSIST-2 Landmark OS Analysis. MPN-111. Presented at the Eleventh Annual Meeting of the Society of Hematologic Oncology. September 6-9, 2023; Houston, Texas.

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