Abstract

Background/Objectives: Sinusoidal obstruction syndrome (SOS), also known as veno-occlusive disease, is a serious complication of hematopoietic stem cell transplantation (HSCT), particularly in high and very high-risk pediatric patients. Despite known risk factors, U.S. data remain limited. The benefit of prophylactic defibrotide is uncertain, with prior trials yielding inconclusive results. This study evaluates its use and association with SOS incidence, healthcare burden, and outcomes. Methods: We performed a retrospective cohort study of 10,250 pediatric HSCT encounters using the Pediatric Health Information System. Patients were stratified as high-risk (n = 9584) or very high-risk (n = 666) per HARMONY criteria. Prophylactic defibrotide was used in 344 encounters; 9906 received none (therapeutic use allowed after SOS diagnosis). Outcomes included SOS incidence, length of stay (LOS), ICU admission, mortality, acute GVHD, and costs. Mixed-effects logistic regression models with patients as a random intercept were used (p < 0.05). Results: SOS incidence differences between the defibrotide prophylaxis and non-prophylaxis groups were not statistically significant in either risk category (high-risk: 26% [n = 79/302] vs. 7.1% [n = 663/9282] p = 0.495, OR 1.457, 95% CI 0.494–4.296; very high-risk: 31.0% [n = 13/42] vs. 21.6% [n = 135/624], p = 0.970, OR 1.081, 95% CI 0.019–60.769). The extremely wide confidence intervals indicate that the data are consistent with both benefit and harm of prophylaxis. Median LOS was longer in the prophylactic group (40 vs. 33 days, p < 0.001; 56 vs. 49 days, p = 0.296, respectively). ICU admissions (50.7% vs. 32.8%; 69.0% vs. 50.8%), mortality (7.9% vs. 3.5%; 23.8% vs. 10.9%), and costs ($443,537 vs. $205,325; p < 0.001) were also higher in the prophylaxis group. Acute GVHD incidence differences were not statistically significant, with contradictory directions between risk subgroups. Conclusions: Prophylactic defibrotide was not associated with reduced SOS incidence and was associated with higher ICU use, longer LOS, increased mortality, and greater costs. These findings represent associations, not causation, and likely reflect residual confounding by indication—as defibrotide prophylaxis was preferentially administered to patients perceived to be at highest clinical risk. Prospective studies with appropriate confounding adjustment are needed to clarify the role of defibrotide in SOS prevention.

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