Vonjo Improves Platelets and Hemoglobin in Patients With Myelofibrosis

More than half of patients with myelofibrosis with low platelets treated with Vonjo had a platelet response, with median platelets rising 58% and hemoglobin increasing.

More than half of patients with low platelets (thrombocytopenia) treated with Vonjo (pacritinib) had a platelet response, with median platelets rising over 50%, and those who responded also saw hemoglobin increase by more than 1 g/dL, while nonresponders’ platelet and hemoglobin levels remained stable, according to study findings published at the 2025 EHA Annual Meeting.

Of the 90 patients, 47 (52.2%) experienced an increase in platelets, known as a platelet response, which means their platelet counts improved according to established criteria. Among these 47 patients, 33 (70.2%) saw this improvement within 90 days. Most patients who responded by day 90 were male or White and had anemia at the start of treatment, similar to those who did not have a platelet response. Patients who responded also had higher platelet counts at the beginning of treatment compared to non-responders.

The median time from myelofibrosis diagnosis to platelet response was 1.7 months overall and 0.9 months for those who responded by day 90. Follow-up after starting treatment was longer in patients who responded (13 months) than in those who did not (11 months). Patients who did not respond had a slightly longer time from diagnosis to treatment start (6.3 months) compared to those who responded (4.9 months).

Treatment with Vonjo was similar between groups, with 42% of responders receiving it as first-line therapy and another 42% as second-line therapy. Among patients with at least nine months of follow-up, the median duration of treatment was six months for those who responded and 5.8 months for non-responders.

Platelet counts in patients who responded increased by a median of 58% by day 90 and remained higher at day 180 (41% increase) and day 270 (32% increase). In patients who did not respond by day 90, platelet counts stayed about the same through day 180 and increased by 14% by day 270. Hemoglobin levels remained stable in both groups through day 180 and increased by 4% in responders and 2.8% in non-responders by day 270.

Six-month survival after day 90 was similar in both groups: 81% in patients who responded and 81% in those who did not, including 14 patients who responded after day 90. Overall survival was consistent between early responders and non-responders, suggesting that longer follow-up is needed to fully understand the survival benefits of a platelet response.

What is the Trial Design?

Researchers reviewed health records of patients with myelofibrosis who were treated with Vonjo in real-world clinical settings between June 2022 and June 2024. The analysis focused on patients with low platelet counts at the start of treatment who had at least three months of follow-up data.

Platelet response was defined as a meaningful increase in platelet counts after starting treatment. Patients who reached this response within three months were highlighted separately.

Researchers also tracked hemoglobin levels and overall survival, which is the length of time patients lived after starting treatment, from three months after treatment began. Outcomes were summarized to show typical experiences with Vonjo in daily practice.

What is Myelofibrosis?

Myelofibrosis is a rare blood cancer that can cause symptoms like fatigue, fever, weight loss, bleeding and bone pain. It can also lead to an enlarged spleen, a risk of progressing to leukemia and shorter life expectancy.

Many patients with myelofibrosis have low platelet counts, which is linked to a higher risk of complications.

Vonjo is a medication approved in the United States to treat patients with myelofibrosis who have very low platelet counts. In clinical studies, Vonjo can help stabilize platelet levels and sometimes improve them, though real-world data on how blood counts respond outside of clinical trials is limited.

Reference

1. “HEMATOLOGIC IMPROVEMENT EXPERIENCED BY PACRITINIB-TREATED PATIENTS WITH MYELOFIBROSIS IN REAL-WORLD CLINICAL SETTINGS,” by Dr. Michael Marrone, et al. 2025 EHA Annual Meeting.

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