Real-world treatment patterns and outcomes in patients with myelofibrosis treated with pacritinib in the United States.

6579 Background: Pacritinib (PAC), a JAK1 sparing JAK2/IRAK1/ACVR1 inhibitor, has shown clinically significant activity in spleen volume and symptom reduction in patients (pts) with thrombocytopenic myelofibrosis (MF). Thrombocytopenic MF is challenging to manage and pts with platelets (PLT) <50 x10 9 /L have limited median overall survival (OS) of 15 months (mo) (Masarova 2018). Since approval as the only agent for thrombocytopenic MF, real-world evidence of PAC use is limited. This study aims to assess treatment patterns, hematological outcomes, and survival in pts with MF treated with PAC in the US. Methods: For this retrospective study, Integra-PrecisionQ de-identified database was used to locate pts with MF (ICD-10: 75.81, D47.4) treated with PAC from 6/1/2022 to 8/31/2023. Treatment-related outcomes include PLT and hemoglobin (Hb) levels from PAC initiation (index) and 30-day intervals post-index. OS was assessed from index through the end of the study period. Data are presented as medians and interquartile ranges (IQR). Results: 142 pts with MF were treated with PAC, the majority being male (60%) or White (66%), with a median age at MF diagnosis of 72 years and median of 13.4 mo from diagnosis to index. In pts receiving ≥2 nd line (2L) PAC (65.5%), the median time from the end of prior MF therapy to PAC initiation was 1 day. Median follow up from index was 6 mo and median exposure to PAC during the observation period was 5.3 mo. In pts with PLT and Hb levels at index and follow up, 28.5% (34/119) had severe thrombocytopenia (PLT<50 x10 9 /L) at index and 29% (35/119) had severe anemia (Hb <8.0 g/dL). Median PLT count was 81 x10 9 /L (47.5,179) at index (n=119) and 96 x10 9 /L (68.5,125) at post-index day 360 (n=15). Median Hb level was 8.8 g/dL (7.9,10.3) at index (n=119) and 10.4g/dL (9.2,11.6) at post-index day 360 (n=15). Increases in PLT and Hb were observed across index PLT and Hb groups over follow up (Table 1). 1-year OS probability was 69.4% (95% CI=56.8-79.0) overall, 77.3% (95% CI=61.5-87.3) in pts treated with 1L PAC, and 75.2% (95% CI=46.3-90.0) for pts treated with 1L PAC with PLT <50 x10 9 /L. Conclusions: In addition to spleen and symptom benefits, real-world outcomes demonstrate stability or improvement in thrombocytopenia and anemia in MF pts treated with PAC, with OS in the 1L setting comparing favorably with other JAK inhibitor historical controls. Table: see text