Defibrotide Prophylaxis of Transplant Associated-Thrombotic Microangiopathy for Neuroblastoma

Inclusion Criteria:

1. Age: 1 - \< 18 years old.
2. Participants must have high-risk neuroblastoma according to Children's Oncology Group (COG) risk classification at the time of initial diagnosis. Participants who were initially considered low or intermediate risk, but then reclassified as high risk are also eligible.
3. Participants may have had salvage therapies (i.e., meta-iodobenzylguanidine (MIBG), dinutuximab) after induction but cannot have progressive disease at start of 4.

   Planned tandem transplants with conditioning with cyclophosphamide-thiotepa and carboplatin-etoposide-melphalan on, or as per, NCT03126916 (ANBL1531) or other tandem-containing COG high-risk neuroblastoma trials.
4. Participants may be enrolled in upfront neuroblastoma protocol, but this is not required.
5. Upfront MIBG or other therapies is not a contraindication.
6. Organ function per institutional standard of care (SOC) guiding clearance for autologous HSCT.
7. Written informed consent (and assent when applicable) obtained from participant or participant's legal representative and ability for subject to comply with the requirements of the study.

Exclusion Criteria:

1. Life expectancy \< 6 months.
2. Pregnant, breastfeeding, or unwilling to practice birth control during participation in the study.
3. Presence of a condition or abnormality that in the opinion of the Investigator would compromise the safety of the patient or the quality of the data.
4. Known bleeding diathesis or bleeding risk deemed by the treating physician to be a contraindication to administration of defibrotide or on concomitant therapeutic anticoagulation. Administration of heparin and/or alteplase for central line maintenance is allowed.