S1643 INCIDENCE, RISK FACTORS AND OUTCOMES OF THROMBOEMBOLISM EVENTS IN HAPLOIDENTICAL VS. MATCHED RELATED DONOR HEMATOPOIETIC STEM CELL TRANSPLANTATION

Background: Allogeneic hematopoietic stem cell transplantation (allo‐HSCT) is regarded as a curative therapy for the majority of malignant hematologic diseases. Only 25–35% of recipients have an HLA‐identical sibling donor. For patients lacking an HLA‐identical donor, a haploidentical donor HSCT (HID‐HSCT) is an alternative option. Patients who undergo HSCT are at a high risk of suffering from thromboembolism events (TEEs) due to the conditioning regimen, immune‐modulatory drugs, graft versus host disease (GVHD) and prolonged hospital stays. However, no information is available on the TEE complication following HID‐HSCT. Aims: To compare discrepancies in the incidence, risk factors and clinical outcomes of TEEs between HID‐HSCT and matched related donor HSCT (MRD‐HSCT). Methods: We retrospectively analyzed data from 5471 HSCT recipients to identify the incidence, risk factors and mortality due to TEEs. TEEs were divided into venous thromboembolism events (VTE) and arterial thrombotic events (ATE). We recorded the incidence and manifestation times of TEEs during the course of HSCT. In the nested case‐based control study, potential risk factors affecting the occurrence of TEEs were identified using univariate and multivariate analyses. Overall survival (OS) was defined as the time elapsed between HSCT day 0 (HSC infusion) and death or the last follow up and was calculated by the Kaplan‐Meier method. Results: Among all 5471 consecutive allo‐HSCT recipients (HID‐HSCT = 3798, MRD‐HSCT = 1673), a total of 117 (2.2%) patients had VTE, including 85 patients after HID‐HSCT and 32 patients after MRD‐HSCT. The incidence of VTE was similar between the two groups (2.2% vs 1.9%). ATE occurred in 45 (0.8%) patients after allo‐HSCT at follow‐up, including 38 patients after HID‐HSCT and 7 patients after MRD‐HSCT. The median occurrence time of VTE after allo‐HSCT was 105 days (range 9–2051). Among the HID‐group, VTE occurred at a median time of 95 days (range 9–1511), which was significantly earlier than that of the MRD‐group (249.5 days, range 14–2053) (p < 0.05). The median occurrence time of ATE after allo‐HSCT was 176 days (range 14–2623). No significant difference was found in the occurrence time of ATE between the MRD and HID‐HSCT groups (p = 0.098). In the univariate analysis, an age >45 years, prior VTE, GVHD, cardiovascular factors and relapse were significantly associated with VTE. In the multivariate analyses, prior VTE, cardiovascular risk factors, aGVHD, and relapse were retained due to their associations with VTE. Both MRD‐HSCT and HID‐HSCT had the same risk factors associated with VTE in the multivariate analysis. The multivariate analysis showed that both a history of GVHD and cardiovascular risk factors were risk factors for ATE after allo‐HSCT. During follow‐up, the probability of overall survival (OS) was 47.1% among patients with TEEs and 76.4% among patients without TEEs (p < 0.05). No significant difference in OS was found between the MRD‐HSCT and HID‐HSCT recipients with TEEs Summary/Conclusion: The incidence of TEEs was similar between MRD‐HSCT and HID‐HSCT. TEEs are highly significant complications for both HID‐HSCT and MRD‐HSCT and have been associated with shorter OS. Well‐designed clinical studies of TEEs prevention and treatment in HSCT recipients are urgently needed.