Ruxolitinib for pediatric patients with treatment-naïve and steroid-refractory acute graft-versus-host disease: the REACH4 study

• Ruxolitinib demonstrated clinically meaningful efficacy in pediatric patients with either treatment-naïve or steroid-refractory aGVHD.

• We identified the ruxolitinib dosage across the pediatric age range treated, and no unexpected safety signals were observed in children.

In REACH4, a phase 1/2, open-label, single-arm, multicenter study, the pharmacokinetics (PK), efficacy, and safety of ruxolitinib were evaluated in treatment-naïve and steroid-refractory pediatric patients with grade 2 to 4 acute graft-versus-host disease (aGVHD; n = 45). Ruxolitinib dosing was based on age and targeted the exposure in adults receiving 10 mg twice daily; group 1 (aged ≥12 to <18 years) received 10 mg twice daily and preliminary starting doses for groups 2 (aged ≥6 to <12 years) and 3 (aged ≥2 to <6 years) were 5 mg twice daily and 4 mg/m² twice daily, respectively. The phase 1 primary objective was to assess ruxolitinib PK parameters and define an age-appropriate recommended phase 2 dose (RP2D) for patients aged <12 years. The phase 2 primary objective was to measure the activity of ruxolitinib as assessed by overall response rate (ORR) at day 28; the key secondary objective was to assess the durable ORR at day 56. Ruxolitinib exposure was comparable across age groups; starting doses were confirmed as the RP2D. The median duration of ruxolitinib exposure was 3.8 months (range, 0.3-11.2). ORR in all patients was 84.4% (90% confidence interval [CI], 72.8-92.5) at day 28, with a durable ORR at day 56 of 66.7% (90% CI, 53.4-78.2); high response rates were observed across age groups and in both treatment-naïve and steroid-refractory subgroups. Adverse events were consistent with those expected in patients with aGVHD (anemia, decreased neutrophil and leukocyte count) treated with ruxolitinib. In pediatric patients with aGVHD, ruxolitinib showed clinically meaningful efficacy with no new safety signals. This trial was registered at www.clinicaltrials.gov as #NCT03491215.