A Multi-Center, Multinational, Prospective Observational Registry Study of Defibrotide in Patients Diagnosed with Severe Veno-Occlusive Disease/Sinusoidal Obstruction Syndrome (VOD/SOS) after Hematopoietic Cell Transplantation (HCT)

Severe hepatic VOD/SOS is a potentially life-threatening complication of HCT conditioning that may also develop after high-dose chemotherapy. The most severe form of VOD/SOS is often accompanied by multi-organ failure (MOF) and is associated with a mortality rate of >80% when managed with supportive care alone. As part of the marketing authorization in Europe, there was an obligation to set up a disease registry of patients with severe VOD/SOS post-HCT who were treated with defibrotide. The goal of this registry was to collect safety and outcome data and assess patterns of defibrotide utilization in the post-approval setting.

This multicenter, multinational, prospective observational study (NCT03032016) was performed by the European Society for Blood and Marrow Transplantation (EBMT). The study included patients with severe VOD/SOS post-HCT who were treated with defibrotide and enrolled from April 2015 to July 2018. Participating centers were members of the EBMT. Physicians registered patients diagnosed with severe VOD/SOS, as assessed by the investigator using classical/standard criteria (including but not limited to hyperbilirubinemia, hepatomegaly, ascites, and weight gain >5%), who consented to participate in the study. In addition, patients who were prescribed defibrotide for purposes other than the approved indication (eg, VOD/SOS prophylaxis, treatment of non-severe VOD/SOS or thrombotic microangiopathy) and consented to participate were registered and information collected. There were no specific exclusion criteria; however, treating physicians were alerted to contraindications, special warnings, and precautions detailed in the defibrotide summary of product characteristics. After inclusion, patient information was collected from participating centers at 100 days, 6 months, and 12 months post-HCT. The primary objective was to assess the incidence of specific serious adverse events (SAEs) of interest, which were hemorrhage and site of bleeding, hypotension, coagulopathy, allergic or hypersensitivity reactions, injection-site reaction, infection and septicemia, and thromboembolic events. Secondary endpoints included Day 100 survival, and overall rate of VOD/SOS (and MOF, if present) resolution (based on standard criteria). Summary statistics were calculated for baseline data and safety variables; outcome analyses are descriptive. Here we report an analysis of data with a cutoff of June 18, 2019. Database lock is planned for October 2019, and the presentation will be updated to include the final data.

A total of 61 patients with severe VOD/SOS were included; MOF was diagnosed at registration in 34 (56%) patients. The median age of patients with severe VOD/SOS was 14.4 (range: 0-68) years, 34 (56%) aged <18 years and 27 (44%) aged ≥18 years. A total of 54 (89%) patients received allogeneic HCT. Primary diseases included acute myeloid leukemia (26%), acute lymphoid leukemia (13%), solid tumor (12%), and myelodysplastic syndrome (8%). The median length of defibrotide exposure was 17 (IQR: 11-25) days.

An SAE of interest occurred in 19 (31%; 95% confidence interval [CI]: 20%-43%) patients with severe VOD/SOS. The most common SAEs of interest by category were infection (n = 13 [21%; 95% CI: 11%-32%]) and bleeding events (n = 8 [13%; 95% CI: 5%-22%]). The most common individual SAEs of interest (≥5% of patients) were pneumonia (8%), gastrointestinal bleeding (8%), and sepsis (5%). Death occurred in 30 (49%) patients within 1 year, with VOD/SOS indicated as a cause of death in 13/30 (43%) patients.

The Kaplan-Meier-estimated survival rate at Day 100 for patients diagnosed with severe VOD/SOS post-HCT who were treated with defibrotide was 74% (95% CI: 61%-83%). At latest follow-up, the survival rate was 51%, with median Kaplan-Meier-estimated survival post-HCT not yet reached. VOD/SOS resolved in 46 (75%) patients; the cumulative rate of VOD/SOS resolution at Day 100 was 87% (95% CI: 72%-94%). Resolution of MOF was achieved in 19/34 (56%) patients who had MOF at VOD/SOS diagnosis.

In conclusion, among patients with severe VOD/SOS post-HCT (with/without MOF), the incidence of SAEs of interest was consistent with that observed in previous defibrotide clinical trials. Treatment with defibrotide resulted in high rates of Day 100 survival and VOD/SOS resolution.