Treatment outcomes in patients with myelofibrosis and platelets ≥50 x10 ⁹ /L treated with pacritinib in the United States.

e18585 Background: Pacritinib (PAC), a JAK1 sparing JAK2/IRAK1/ACVR1 inhibitor, has shown clinically significant spleen volume and symptom reduction in patients (pts) with myelofibrosis (MF). While PAC is approved for use in pts with MF and severe thrombocytopenia, real-world data show PAC has been used for MF treatment in pts with higher platelet counts (PLT). Here, we report real-world treatment outcomes in pts with MF who presented with PLT≥50x10^9/L at PAC initiation. Methods: A retrospective analysis was conducted of de-identified data from Integra-PrecisionQ database (roughly 80% US community oncology practices) of pts with MF and platelet counts (PLT) ≥50 x10 9 /L at PAC initiation from 6/1/2022 to 6/30/2024. Treatment patterns, PLT, and overall survival (OS) were assessed from PAC initiation (index) through the end of the study period. Data are presented as medians and interquartile ranges (IQR) overall and by PLT 50-100 x10 9 /L and PLT >100 x10 9 /L. Results: Of 212 pts with MF treated with PAC, the majority were male (57.5%), White (62.7%), and the median age at MF diagnosis was 73 years. With a median follow-up of 10 months from index to the end of the study period, the median duration of PAC use was 6 months for pts with ≥9 months of follow-up data (n=111). Of 179 pts with PLT data at index and follow-up, 66% (118/179) had PLT ≥50 x10 9 /L at index. The median (IQR) time from MF diagnosis to index was 7.7 months overall (0.5, 43.3), 10.4 months (1.8, 47) for pts with PLT 50-100 x10 9 /L and 14.4 months (3.9, 60.6) for pts with PLT >100 x10 9 /L. Similar percentage of pts received PAC in the first-line (1L) (40%; 85/212) and second-line (2L) settings (41%; 86/212) overall and in the subset with PLT 50-100 x10 9 /L (39% 1L and 46% 2L). However, pts with PLT >100 x10 9 /L were less likely to receive PAC in the 1L setting (27% 1L and 44% 2L). Overall, median PLT count was 72 x10 9 /L (37.5, 167) at index (n=179) and 86.5 x10 9 /L (31, 138) at post-index day 360 (n=30) (Table). PLT remained stable in pts with PLT 50-100 x10 9 /L or PLT >100 x10 9 /L from index through day 360 (Table). The OS from index through the end of the study period was 68% (144/212) overall, 65% (35/54) in pts with PLT 50-100 x10 9 /L, and 83% (53/64) in pts with PLT >100 x10 9 /L. OS probability at 12 months was 69% (95% confidence interval [CI]=61.5-75.3) overall, 69% (95% CI=53.4-80.3) in pts with PLT 50-100 x10 9 /L and 78.4% (95% CI=64.1-87.6) for pts with PLT >100 x10 9 /L. Conclusions: Real-world treatment outcomes demonstrate stability or improvement in PLT values in pts with MF and PLT ≥50 x10 9 /Ltreated with PAC. Median (IQR) PLT (x10 9 /L) overall and by index platelet count. N Overall N PLT 50-100 N PLT >100 Index 179 72 (37.5, 167) 54 72 (60, 84) 64 240 (158, 418) Day 90 125 89 (38, 186) 35 87 (60, 113) 48 249.5 (122.5, 444) Day 180 109 75 (43, 147) 32 73.5 (52, 114.5) 40 240.5 (122, 404) Day 360 30 86.5 (31, 138) 7 93 (48, 119.5) 7 199 (88, 251.5)