Comparison of Splenectomy and Treatment Failure Incidence in Nonsplenectomized Patients with Immune Thrombocytopenia (ITP) Receiving Romiplostim or Medical Standard of Care: 1-Year Treatment and 6-Month Safety Follow-up.

Abstract 679

Chronic ITP is an autoimmune disease characterized by low platelet counts due to both increased platelet destruction and suboptimal platelet production. Immunosuppressive ITP therapies have variable response rates and may be associated with substantial side effects, limiting their use for long-term treatment. Romiplostim is a novel peptibody that increases platelet counts by a mechanism similar to thrombopoietin, and is approved for the treatment of chronic ITP. We present final results from a phase 3b, randomized, open-label study, comparing the incidence of splenectomy and treatment failure in adult nonsplenectomized ITP patients receiving either romiplostim or medical standard of care (SOC). Patients were randomized (2:1) to romiplostim or SOC. Eligible patients had a platelet count <50 × 10⁹/L. Once-weekly subcutaneous romiplostim was administered with dose adjustments to target a platelet count between 50 and 200 × 10⁹/L. SOC treatments were prescribed according to standard institutional practices or therapeutic guidelines; the only treatments not allowed were investigational agents (rituximab was allowed) or other thrombopoietic agents. Patients received romiplostim or SOC for 52 weeks, and those who did not subsequently transfer to another romiplostim study completed a 6-month off-treatment safety follow-up. Co-primary endpoints of the study were: the incidence of splenectomy and the incidence of treatment failure (defined as: platelet count ≤20 × 10⁹/L for 4 consecutive weeks at the highest recommended dose and schedule, or major bleeding event, or change in therapy due to intolerable side-effect or bleeding symptoms). Patients who discontinued study during the treatment period were counted as having had splenectomy or treatment failure. To assess the impact of treatment discontinuation on the primary endpoints, a sensitivity analysis was conducted to determine the actual incidence of splenectomy or treatment failure.

A total of 234 patients were randomized (romiplostim, 157; SOC, 77); 83% of romiplostim and 66% of SOC patients completed the study. Patients had been diagnosed with ITP for a median of 2 years (range 0.01 to 44 years) and 73% had received ≥2 prior ITP therapies. Patient characteristics were similar between treatment groups. The efficacy of romiplostim was significantly greater than that of SOC in both primary endpoint analyses. The incidence of splenectomy was 9% (14/157) in the romiplostim group compared to 36% (28/77) in the SOC group (OR, 0.17; 0.08, 0.35; p<0.0001), and the incidence of treatment failure was 12% (18/157) in the romiplostim group compared to 30% (23/77) in the SOC group (OR, 0.31; 0.15, 0.61; p=0.0005). Sensitivity analyses confirmed the primary endpoint analyses: the actual incidence of splenectomy was significantly lower in the romiplostim group (2/157, 1%) than the SOC group (15/77, 20%) [p<0.0001], and the actual incidence of treatment failure was significantly lower in the romiplostim group (6/157, 4%) than the SOC group (10/77, 13%) [p=0.009]. The incidence of bleeding events with a worst grade score ≥3 appeared lower for patients in the romiplostim group (3%) than the SOC group (7%). Safety analyses included only patients who received ≥1 dose of romiplostim or 1 type of SOC. During the 52-week treatment period, adverse events occurred in 96% (147/154) of patients receiving romiplostim and 92% (69/75) of patients receiving SOC. Serious adverse events occurred in 23% (35/154) of romiplostim and 37% (28/75) of SOC patients; serious adverse events were considered treatment-related in 5% (7/154) of romiplostim and 8% (6/75) of SOC patients. During the 6-month safety follow-up period, 36% (11/31) of romiplostim and 43% (18/42) of SOC patients experienced an adverse event; treatment-related adverse events occurred in none of the romiplostim patients and 2 of the SOC patients. Overall, 6 patients died: 1 (1%) in the romiplostim group and 5 (7%) in the SOC group. None of the deaths were considered related to study treatment or the underlying ITP. No patients tested positive for neutralizing antibodies to romiplostim or TPO. One romiplostim-treated patient showed an increase in bone marrow reticulin that was still within the normal range (Grade 2). In summary, romiplostim significantly reduced incidences of splenectomy and treatment failure in nonsplenectomized ITP patients compared to SOC. The safety profile of romiplostim was similar to SOC.