Updated Results from the Single-Arm, Open-Label, Long-Term Efficacy and Safety Study of Subcutaneous (SC) Romiplostim in Children with Immune Thrombocytopenia (ITP)

▪ Background: Romiplostim, a thrombopoietin (TPO) receptor agonist approved for children and adults with chronic ITP, was evaluated in children with ITP in a ≤3-year open-label trial. Interim results were previously reported (Grainger et al., Blood 2017 130:2334). Here we present updated results as of 27 Mar 2019. Methods: Eligible children from 17 countries with ITP for ≥6 months and screening platelet count ≤30×109/L (or uncontrolled bleeding) received SC romiplostim (1 μg/kg titrated to 10 μg/kg to maintain platelet counts of 50-200×109/L). In Europe, bone marrow was evaluated at baseline and after 1 (day 365 ± 4 weeks) or 2 (day 730 ± 4 weeks) years. The primary endpoint was % time with a platelet response (platelet count ≥50×109/L, no rescue therapy in preceding 4 weeks) in months 0-6. Results: A total of 203 patients (pts) received ≥1 dose; the median (interquartile range [IQR]) age was 10 (6-13) and median (IQR) platelet count 14 (7-23.5×109/L). The median (IQR) duration of treatment was 145 (39-156) weeks, median (IQR) % of time with a platelet response in months 0-6 was 50% (17-83%), with 88% (179/203) of pts having a platelet response at least once (Fig. 1A). In all pts, the median (IQR) % of time with an increase in platelet counts ≥20×109/L above baseline from week 2 until the end of treatment was 79% (39-92%). Median and lower quartile platelet counts were both consistently >50×109/L from week 12 and 48, respectively, and did not vary by age. Eleven pts maintained platelet counts ≥50×109/L without ITP medications (including romiplostim) for ≥24 weeks; median (IQR) time to onset was 50 (24-80) weeks after starting romiplostim. During the study, 60 (30%) pts received rescue therapy, typically within weeks 1-36, and 3 underwent splenectomy. With a total exposure of 428.7 patient-years, median (IQR) average weekly romiplostim dose over the entire study was 6.9 (4.6-8.9) µg/kg; 8.5 (5.0-10.0) μg/kg at 1 year (n=144) and 6.0 (3.0-10.0) μg/kg at 2 years (n=129; Fig. 1B). Self-administration was initiated in 68% of pts. Ninety-five pts (46.8%) discontinued treatment: reasons included lack of efficacy (n=43 [21.2%]), patient request (n=15 [7.4%]), adverse event (AE; n=9 [4.4%]), and neutralizing antibodies (NAb; n=7 [3.4%]). AEs occurred in 192 pts (94.6%); the most frequent were epistaxis (38.4%), headache (37.9%), and nasopharyngitis (36.9%). Serious AEs (SAEs) occurred in 59 (29.1%) pts, including epistaxis (5.9%), decreased platelet count (4.4%), a