Effect of Romiplostim on Health-Related Quality of Life in Children with Immune Thrombocytopenia and Associated Burden in Their Parents: Results from a Phase 3, Randomized, Double-Blind, Placebo-Controlled Study

Background: Immune thrombocytopenia (ITP) is an autoimmune disorder characterized by low platelet count levels and increased risk of bleeding. Symptomatic ITP in children can have a negative impact on their health-related quality of life (HRQoL) and increase their parents' burden. The effect of romiplostim (a thrombopoietin receptor agonist) on HRQoL and parental burden was evaluated in a phase 3 study of children with ITP.

Methods: In a phase 3, randomized, double-blind, placebo-controlled study on efficacy and safety of romiplostim, children (<18 years) with ITP ≥ 6 months were randomized to weekly romiplostim or placebo for 24 weeks. The Kids' ITP Tool (KIT), a psychometrically-valid disease-specific HRQoL instrument (Klaassen Ped Blood Cancer2007), was administered to children and/or their parents at baseline, weeks 8, 16, and 25. All three KIT versions were used: Child self-report (to assess HRQoL of children ≥7 years), Parent/Proxy (to assess HRQoL of children <7 years via parent proxy), and Parent self-report (to assess impact of children's ITP on parental burden, for children of all ages). Each KIT version contains 26 items, summarized in a single score ranging from 0 to 100. Higher Child or Parent/Proxy KIT scores reflect better HRQoL of a child with ITP, and higher Parent KIT scores reflect less parental burden.

Among efficacy endpoints of the study, overall platelet response was defined as achieving a weekly platelet response (platelet count ≥ 50 x 10⁹/L) for ≥ 4 weeks during weeks 2 to 25, and durable platelet response was defined as achieving a weekly platelet response for ≥ 6 weeks during weeks 18 through 25.

As exploratory endpoints of the study, changes in KIT scores from baseline to each follow-up assessment were estimated separately by treatment group (romiplostim or placebo) and by overall/durable platelet response status (yes/no). A mixed effects repeated measures analysis was conducted to estimate the difference in changes of Child and Parent KIT scores between romiplostim group and placebo group, controlling for baseline score, child's age, child's gender, and child's race (analysis of Parent/Proxy data was not conducted due to small sample size).

Results: Sixty-two patients were enrolled and randomized to receive romiplostim (42 patients) and placebo (20 patients). Mean age was 9.6 years (range: 3-17, 16 patients <7 years), 57% were female, and 66% were white. Overall and durable platelet response was achieved by 34 and 24 patients, respectively.

In general, changes in KIT scores by treatment group and overall platelet response status showed numerically greater and more often statistically significant improvements from baseline to each assessment for children receiving romiplostim (vs placebo) and for platelet responders (vs non-responders) (see Tables 1 and 2). Results based on durable response status were similar to those based on overall response status (data not shown).

In the mixed effects analysis, greater improvement from baseline to week 8/16/25 on Parent KIT score was found in the romiplostim group vs placebo (by approximately 8 points, p-value<0.05); no significant difference was found between groups for Child KIT score.

Conclusion: Romiplostim treatment is associated with reduced parental burden (measured by Parent KIT score). In some instances sample sizes were small for other KIT versions; therefore, results should be interpreted with caution.