P827: EFFICACY AND SAFETY OF ROMIPLOSTIM ADDED TO IMMUNOSUPPRESSIVE THERAPY AS A FIRST-LINE TREATMENT IN PATIENTS WITH APLASTIC ANEMIA: A PHASE 2/3 CLINICAL TRIAL

Abstract

Background: Romiplostim, a thrombopoietin (TPO) mimetic protein, has been shown to promote tri-lineage hematopoiesis in patients with acquired aplastic anemia (AA) refractory to immunosuppressive therapy (IST) or eltrombopag; however, its effectiveness in the combination therapy with antithymocyte globulin (ATG) plus cyclosporine (CsA) as a first-line treatment remains unknown. Aims: To clarify this issue, we conducted a phase 2/3 clinical trial to evaluate the efficacy and safety of romiplostim combined with rabbit ATG plus CsA in patients with AA requiring transfusions who had not been exposed to IST. Methods: This study was a multi-national, open-label study with romiplostim in IST-naïve adult patients with AA (NCT03957694). 10 µg/kg of romiplostim was started on day 1 of ATG therapy (2.5mg/kg/day for 5 days) and was weekly given for the first 4 weeks. The dose was adjusted from 5 to 20 µg/kg according to the prespecified dose adjustment procedure. Treatment lasted until Week 26. For those who intend to continue treatment, romiplostim administration was extended to Week 52. The primary endpoint was the hematological response rate (HRR) at Week 27 based on the response assessment criteria (Table 1). The secondary endpoints included the HRR at Week 14; the time to the hematological response; the proportion of patients who achieved transfusion independence or who showed a reduction of transfusion requirement among patients who had received a transfusion within 8 weeks prior to the first romiplostim administration. The bone marrow and cytogenetic analyses were performed prior to enrollment and at Week 27 and 53. Results: Twenty-six patients were screened, of which 17 (9 Japan, 7 Korea, and 1 Taiwan; 5 transfusion dependent non-severe AA, 6 severe AA (SAA) and 6 very SAA) were enrolled in the study. The median age was 44.0 years (range: 25-70). Two patients discontinued romiplostim before Week 27. The HRR (CR or PR) at Week 27 was 76.5% (95% CI: 50.10%, 93.13%), of which 6 (35.3%) achieved CR. The HRR at Week 14 was 41.2% (95% CI: 18.44%, 67.03%). The median day to achieve the first hematological response was 93.0 (range: 63-181). Of the 16 patients who depended on platelet transfusion before romiplostim administration, 14 (87.5%) achieved transfusion independence or showed a reduction of transfusion requirement at Week 27. In addition, of 16 who required erythrocyte transfusion at baseline, 13 (81.3%) achieved transfusion independence or showed a reduction of transfusion requirement at Week 27. The frequently reported adverse events (AEs) were constipation (41.2%) followed by headache (35.6%). The frequently reported drug-related AEs were headache (12.9%) followed by muscle spasms (9.7%), alanine aminotransferase increased, fibrin D dimer increased, malaise, and pain in extremity (each 6.5%). In bone marrow examination, increases of reticuline grade (grade 1 to 2) were observed in 3 patients at Week 27 and 1 patient at Week 53. No chromosomal abnormality or transformation into MDS and/or AML was observed. Image:Summary/Conclusion: This is the first clinical trial of romiplostim combined with rabbit ATG plus CsA in patients with acquired AA requiring transfusions who were previously untreated with IST. This regimen produced higher HRR at Week 27 (76.5%) than those of historical control received rabbit ATG plus CsA (approximately 50% at 6 months), with manageable AEs, and could therefore serve as a new first-line treatment option in patients with AA.