SAN DIEGO, CA—Jeffrey Wasser, MD, from the Department of Medicine, Division of Hematology-Oncology, University of Connecticut School of Medicine, Farmington, and colleagues report at the 53rd American Society of Hematology Annual Meeting and Exposition that romiplostim may have greater effects on platelet responses than standard of care (SOC) + rituximab or SOC alone in immune thrombocytopenia (ITP).

In a previous open-label, 52-week trial, romiplostim, a thrombopoietin mimetic, was compared to SOC in ITP patients without prior splenectomy and was shown to have a lower percentage of treatment failure (4% vs 13%, P<0.001, respectively), as was splenectomy (1% vs 20%). Eleven of 16 patients in the SOC arm received rituximab 219–363mg/m2 once weekly for four weeks.

In this post hoc, non-randomized comparison, investigators examined outcomes of these 16 patients as compared with the romiplostim group (in which one patient received rituximab) and the SOC arm as a whole. Patients were categorized into three treatment groups: romiplostim, SOC + rituximab, and SOC alone. Baseline characteristics such as age, sex, and platelet count were comparable between all three arms.

Patients in the romiplostim and SOC arms had a shorter median ITP duration than patients in the SOC + rituximab arm (2.1, 2.3, vs 3.4 years, respectively). When comparing the romiplostim-treatment group vs. the SOC+ rituximab and SOC alone groups, a greater percentage of romiplostim patients completed the full 52-week trial (78% vs. 44%, 56%, respectively) and also experienced fewer treatment failures (4% vs 13%, 13%, respectively). Romiplostim also demonstrated higher platelet response rates (platelet count >50×109/L, excluding eight weeks after rescue medication) than SOC + rituximab or SOC as a whole. Adverse event rates were similar for all three groups.

In the SOC + rituximab group, there was no change in the proportion of patients receiving concomitant ITP medications or the number of medications per patient in the time prior to receiving rituximab compared with during or after rituximab treatment. The most common concomitant medications were prednisone, IVIg, anti-D, and methlyprednisone (during or after rituximab).

After analysis of the study data, Dr. Wasser concluded that romiplostim may have greater effects on platelet responses than SOC + rituximab or SOC alone. However, he does note, “Different treatment goals make efficacy comparisons problematic, particularly as the long-term response rate was not measured in this one-year study.” Additionally, the change in use of concomitant ITP medications over the course of the study was also not analyzed. Because significant morbidity and mortality is associated with splenectomy and immunosuppressive ITP medications, this is an important consideration. Most important to note, the non-randomized selection of patients by the investigators, evidenced by the longer duration of ITP, make any generalizations difficult. Dr. Wasser and his colleagues believe that prospective controlled studies of romiplostim and rituximab in patients with ITP would be needed to provide further information.