Background: Recent studies have reported that the outcomes after haploidentical donor (HID) hematopoietic stem cell transplantation (HSCT) are comparable to those after matched related donor (MRD) HSCT in hematological disease patients. Hepatic sinusoidal obstruction syndrome (SOS) is a rare but lethal complication with a reported incidence of 8%~14% and a mortality rate higher than 80% for the severe type of SOS after MRD HSCT. Although sufficient information is available on SOS after MRD HSCT, few studies have systematically investigated SOS after HID HSCT. Here, we conducted a retrospective multicenter study in China to assess the incidence, clinical characteristics, risk factors and transplant outcomes of SOS following HID HSCT. Aims: The aim of this study is to compare the incidence, clinical characteristics, risk factors and transplant outcomes of SOS after HID HSCT and MRD HSCT. Methods: We retrospectively evaluated 36 consecutive patients with a confirmed diagnosis of SOS after allogeneic HSCT (allo-HSCT) (HID: 23 patients, MRD: 13 patients) at four large HSCT centers in China between January 2003 and July 2018. The diagnosis of SOS was based on clinical criteria that required the occurrence of two of the following events: hyperbilirubinemia (≥ 2 mg/dL), hepatomegaly or right upper quadrant pain of hepatic origin, or unexplained weight gain (> 2% of baseline body weight) due to fluid accumulation. The SOS severity was defined as mild, moderate, severe or very severe. Kaplan-Meier survival analysis was used to estimate the cumulative incidence of relapse, overall survival (OS) and transplant-related mortality (TRM), and a log-rank test was performed to assess the statistical significance. Cox regression analysis was used to identify potential risk factors affecting the occurrence of SOS. Results: SOS developed in 0.4% of the patients (HIDs: 0.4%, MRDs: 0.5%, p = 0.952) at a median time of 21.50 days (range, 1-55) after allo-HSCT. No significant difference was found between the two groups in gender, disease distribution, interval from diagnosis to HSCT, disease status at the time of HSCT, donor-patient sex match, donor-patient ABO match, stem cell source, follow-up time, engraftment time and cumulative incidence of acute graft-versus-host disease (GVHD) or chronic GVHD. The HID and MRD groups were comparable in terms of the median time to diagnosis (HIDs: 24 days, MRDs: 20 days, p = 0.316) and the presentation and severity of SOS. For patients diagnosed with SOS, the 2-year cumulative incidences of relapse were 22.7% and 22.4% in patients receiving HID and MRD transplantations, respectively (p = 0.584). OS at 2 years was 10.4% and 38.5% in the two groups, respectively (p = 0.113). The TRM at 100 days was 60.9% in the HID group and 38.5% in the MRD group (p = 0.178).
