P1608: real-world insights on the management of immune-mediated thrombotic thrombocytopenic purpura (ittp) with caplacizumab in belgium

Topic: 32. Platelet disorders Background: Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is a rare, life-threatening disorder, caused by autoantibody-mediated deficiency of a disintegrin and metalloproteinase with thrombospondin type 1 motif, member 13 (ADAMTS13). Real-world data from Germany, France, and the United Kingdom confirm that caplacizumab allows rapid recovery of iTTP. Caplacizumab has been commercialized and reimbursed in Belgium since September 1, 2019. Real-world data on the treatment of iTTP patients with caplacizumab in Belgium are lacking. Aims: To provide real-world data on the use of caplacizumab in Belgium. Methods: This retrospective study analyzed hospital chart review data for patients with iTTP (≥18 years old) who were hospitalized and treated with caplacizumab in 13 Belgian hospitals (September 1, 2019, to January 15, 2022). Patients were included if they had caplacizumab treatment initiated and ended within the study period. Patient demographics, treatment characteristics, efficacy and safety outcomes, and healthcare resource utilization are presented. To identify differences in disease management, analyses were performed in 2 subgroups: first diagnosed episodes and relapse episodes. Results: A total of 39 iTTP episodes (25 first diagnoses, 14 relapse episodes) were identified in 33 patients (18–89 years old) who were treated with caplacizumab (Table). Females developed 21 episodes and males developed 18 episodes, with a higher proportion of females than males in the relapse episode subgroup (71.4% vs 28.6%). Mean (standard deviation [SD]) number of doses of caplacizumab per episode was 39.2 (14.7) for first diagnosed episodes and 31.9 (8.4) for relapse episodes. Caplacizumab was initiated quickly after hospital admission for first diagnosed episodes (2.7 days) and relapse episodes (0.4 days). Caplacizumab was generally initiated on the same day as iTTP diagnosis confirmation by ADAMTS13 activity-testing (level <10%); 2 centers started treatment before disease confirmation due to delayed results. Mean (SD) duration of hospital stay was 16.0 (10.3) days for first diagnosed episodes and 9.1 (2.9) days for relapse episodes. Exacerbation was observed in 2/39 (5.1%) episodes and relapse occurred in 6/39 (15.4%) episodes. Treatment was interrupted at the time both exacerbations occurred because there was a lack of symptoms of ongoing disease; 1 patient did not have ADAMTS13-testing at time of interruption and 1 had ADAMTS13 level <10%. Of 6 patients who developed a relapse, 3 patients in the first diagnosis subgroup had a short time (~7 days) between termination of caplacizumab in their first reported episode and relapse; treatment was stopped in these patients due to platelet count normalization and symptom resolution, however, ADAMTS13 was <10%. No patients were refractory to treatment or passed away. Bleeding events occurred in 3/25 (12.0%) and 2/14 (14.3%) of episodes in the first diagnosis and relapse episodes, respectively. Summary/Conclusion: Caplacizumab was initiated quickly after hospital admission in combination with therapeutic plasma exchange and immunosuppressive therapy. Although ADAMTS13 testing is well established at diagnosis, our results show that additional ADAMTS13 testing should be used to optimize treatment and guide treatment discontinuation. Exacerbations and relapses may have been avoided if treatment duration was tailored to normalization of ADAMTS13 activity. Our results are in line with other published real-world data. Disease management of iTTP in Belgium is in line with international ISTH guidelines and caplacizumab is used as front-line therapy.Keywords: ADAMTS13, Platelet, Bleeding disorder, Thrombotic thrombocytopenic purpura (TTP)