Sinusoidal obstruction syndrome (SOS), formerly known as hepatic veno-occlusive disease (VOD) is a serious complication of hematopoietic cell transplantation (HCT). Although it has been described following both autologous and allogenic HCT, it seems much more frequent following the latter, with a reported incidence of 8 to 14%. This can dramatically increase in high risk populations. The pathophysiology of VOD/SOS involves activation and lesion, often multifactorial, of sinusoidal endothelial cells, permeabilization of the endothelial barrier with penetration of blood cells and cellular debris into the space of Disse leading to the narrowing of the sinusoidal lumen, and the development of a post-sinusoidal portal hypertension . The risk factors are related to the transplant, to the patient or disease characteristics, or to liver status before HCT. Of note, hepatic status risk factors are previous history of hepatic disease such as cirrhosis or active viral hepatitis, elevation of transaminases or bilirubin, iron overload, hepatic irradiation or treatment with the recently introduced hepatotoxic drugs such as gentuzumab ozogamicin or inotuzumab ozogamicin.

From the therapeutic standpoint, defibrotide has been approved recently for the treatment of severe SOS/VOD. The advent of defibrotide has rejuvenated the research in this field of orphan complications after HCT. This web focus collection aims to gather the most recent report published in the area, with the aim to stimulate interactions and enhance research effort in this field.