The purpose of this study is to (1) demonstrate the efficacy and safety (toxicity) of 25 mg/kg/day of Defibrotide in patients with severe veno-occlusive disease (sVOD) and (2) evaluate serum and endothelial markers of veno-occlusive disease (VOD) through the analysis of blood samples.

This is a historically-controlled, multicenter, open label Phase 3 study to determine the safety and efficacy of 25 mg/kg/day of Defibrotide (DF) for the treatment of severe VOD in hematopoietic stem cell transplantation (HSCT) patients.

In this study, the term "severe VOD" is defined as those patients who meet the Baltimore diagnostic criteria for VOD (total bilirubin >/= 2.0 mg/dL plus two of the following: ascites, >/=5% weight gain and hepatomegaly), who also have multi-organ failure (i.e., pulmonary and/or renal dysfunction). This represents a group of patients in whom mortality at Day+100 has been estimated to be >80%.

Comparisons: The primary parameter is Complete Response at 100 days following stem cell transplant, utilizing historical controls as a comparator. The historical control database will be generated through a retrospective medical chart review performed at participating centers; the survival outcome of patients who would otherwise have met eligibility criteria for this trial will be compared to the survival observed in patients prospectively treated with Defibrotide. Secondary parameters include survival rate at 100 days and 6 months post stem cell transplantation (SCT), and special studies of endothelial and serum markers for VOD. This study will assess safety of the dose and schedule in this setting.

Inclusion Criteria:

• Clinical diagnosis of VOD, defined by jaundice (bilirubin >/= 2 mg/dL) and at least 2 of the following clinical findings, by Day+21 post stem cell transplant: ascites; weight gain >/= 5% above baseline weight; hepatomegaly.
• Severe VOD, defined as VOD with multi-organ failure, i.e., presence of one or both of the following, by Day+28 post stem cell transplant: renal or pulmonary dysfunction.
• Provide voluntary written informed consent.

Exclusion Criteria:

• Pre-existing (prior to SCT) cirrhosis
• An alternative diagnosis for weight gain, ascites and jaundice
• Graft-versus-host disease (GVHD) grade B or higher involving liver or gut or grade C or higher involving skin
• Prior solid organ transplant
• Dependent on dialysis prior to and/or at the time of SCT
• Dependent on oxygen supplementation prior to SCT
• Significant acute bleeding or hemodynamic instability
• Requirement for the use of any medications that increase risk of hemorrhage will be excluded from the treatment group