Real-World Use of Recombinant Von Willebrand Factor in People with Clinically Severe Congenital Von Willebrand Disease: Interim Analysis of Athn 9: A Natural History Study for People with Severe VWD

Background: People with von Willebrand disease (VWD) present with a spectrum of bleeding patterns and clinical symptoms, independent of subtype (Rugeri. Haematologica. 2007; Kalot. Haemophilia. 2021). In certain situations, prophylaxis may be appropriate, particularly when there is recurrent and severe bleeding (Connell, Blood Advances, 2021). There are limited real-world data on the use of recombinant von Willebrand factor (rVWF) in the United States.

Aim: To characterize the safety and real-world effectiveness of routine prophylaxis with rVWF in people with clinically severe congenital VWD.

Study Design and Methods:This is an interim analysis of a phase 4, longitudinal, prospective, observational cohort study (NCT03853486). Participants with severe VWD types 1, 2, and 3 (≤30% of normal) or “clinically severe VWD” (≤40% of normal with severe bleeding and requiring prophylaxis with factor concentrates) were identified from the ATHNdataset. The American Thrombosis & Hemostasis Network (ATHN) is the steward of the ATHNdataset, a Health Insurance Portability and Accountability Act-compliant, de-identified patient health dataset containing data from individuals with bleeding disorders receiving care through ATHN affiliates who opt in to contribute. Treatment regimens were at the discretion of each participant's respective bleeding disorder provider. Participants are followed for 2 years from the time of enrollment. Safety was measured using definitions from the European Haemophilia Safety Surveillance program. Bleeding events (BEs) were measured by individual bleeding components and calculated per the International Society on Thrombosis and Haemostasis Bleed Assessment Tool and/or the Pictorial Bleeding Assessment Chart. Health-related quality of life measures, including an ATHN9 rVWF substudy form, were used to describe real-world effectiveness of rVWF treatment. Descriptive statistics were used to analyze study outcomes. This study was not designed to detect differences in safety or efficacy between individual treatment products.

Interim Results:As of June 16, 2023, 23 participants enrolled in the ATHN9 study were receiving rVWF; 14 participants have been prescribed rVWF for at least 1 full year, 13 of whom received continuous prophylaxis. This abstract reports on those 13 participants in the first year of the study. Mean (SD) age was 42.9 (29.2) years; 69.2% (n=9) of participants were female. Most participants had no comorbidities. As expected, most participants had a family history of VWD (84.6%; n=11) and no documented VWF inhibitors (84.6%; n=11); inhibitor status for the remaining 2 participants was unknown. Baseline VWF and factor VIII measurements were reported for most participants ( Table 1). The majority had type 2 VWD (84.6%; n=11), 92.3% (n=12) had identifiable genetic sequence defects in VWF, and 30.8% (n=4) had an abnormal VWF multimer profile. As dictated by the local investigator, rVWF prophylactic regimens ranged from 36.6 IU/kg once weekly to 57.6 IU/kg every 3 days; 7 (53.8%) participants received 40-60 IU/kg at a frequency of 2-3 times per week. Twenty-one BEs occurred in 5 (38.5%) of the participants receiving rVWF prophylaxis during the first year ( Table 2). Most BEs were spontaneous (61.9%; 13/21), occurring in the nose (n=7), gastrointestinal tract (n=5), or ankle (n=1). The remaining BEs were associated with activity with no known trauma (n=4), trauma (n=2), or unknown cause (n=2). One participant reported 3 rVWF treatment-unrelated adverse events (AEs) of humerus shaft closed fracture, metabolic encephalopathy, and acute exacerbation of chronic obstructive airways disease. When surveyed about their experience with rVWF, participants reported very or extremely satisfied as follows: 76.9% (n=10) with infusion time, 84.6% (n=11) with breakthrough bleed control time, 46.2% (n=6) with number of infusions required for breakthrough bleed control, and 69.2% (n=9) with frequency of achieving bleed control without concomitant hemostatic medication.

Discussion:In participants with clinically severe congenital VWD, continuous prophylaxis with rVWF was associated with minimal AEs. Most participants receiving rVWF prophylaxis experienced no BEs during the first year of the study. Most participants expressed overall satisfaction with the use of rVWF.