Spleen Volume Reduction Predicts OS in Myelofibrosis Treated with Pacritinib

By Keightley Amen - Last Updated: June 11, 2023

A study presented at the 2023 American Society of Clinical Oncology Annual Meeting found that spleen volume reduction predicts overall survival (OS) in patients with myelofibrosis who are taking pacritinib, but that the same was not true for patients receiving “best available therapy.”

In patients with myelofibrosis, JAK2 inhibitors can reduce spleen volume, which is often an indicator of the disease’s response to treatment. However, the relationships are not fully understood. “For example … ruxolitinib cannot be administered at full dose in patients with lower platelet counts, and it is not known whether the association between spleen volume reduction and overall survival persists in such patients,” wrote the authors, led by Helen Ajufo, MD, of Memorial Sloan Kettering Cancer Center in New York, New York.

Pacritinib is a JAK inhibitor which was shown in the PERSIST-2 trial to induce spleen volume reduction better than “best available treatment,” including ruxolitinib. The current study was a retrospective analysis of those data to elucidate OS. This analysis included patients who were alive and still taking part in the study at week 10, when the window opened for examination of spleen reduction, assessed by magnetic resonance imaging or computed tomography.

Of the patients receiving pacritinib (n=89), any reduction in spleen volume at 12 weeks was significantly associated with improved survival. However, in patients on “best available therapy,” spleen volume reduction did not predict a benefit in OS (n=84). To illustrate this, 11% (3 of 28) of patients receiving “best available therapy” who achieved spleen volume reduction of 10% or more died, which was similar to non-responders (14%, or 8 of 56).

As PAC can be given at full dose regardless of PLT count, it is possible that PAC may offer a unique survival advantage for MF patients with moderate or severe thrombocytopenia who achieve spleen reduction,” the authors concluded.


Ajufo H, Bewersdorf JP, Harrison C, et al. Spleen volume reduction (SVR) predicts overall survival (OS) in myelofibrosis (MF) patients on pacritinib (PAC) but not best available therapy (BAT): PERSIST-2 landmark OS analysis. Abstract #7018. Presented at the 2023 American Society of Clinical Oncology Annual Meeting; June 2-6, 2023; Chicago, Illinois.

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