Venous thromboembolism is associated with graft--host disease and increased non-relapse mortality after allogeneic hematopoietic stem cell transplantation.

Although venous thromboembolism rates and risk factors are well described in patients with cancer, there are limited data on the incidence, risk factors and outcomes of thrombosis after allogeneic stem cell transplantation, a curative therapy for patients with hematologic malignancies. We aimed to determine the incidence and risks associated with venous thrombosis in allogeneic stem cell transplants. We studied 2276 recipients of first transplant between 2002-2013 at our institution with a median follow up of 50 months (range 4-146). Using pharmacy records and subsequent chart reviews, 190 patients who received systemic anticoagulation for venous thrombosis were identified. The 1-and 2-year cumulative incidence of all venous thrombotic events were 5.5% (95% confidence interval (CI) 4.6-6.5%) and 7.1% (95% CI 6.1-8.2%), respectively. There was no difference in age, sex, body mass index, diagnosis, disease risk index, conditioning intensity, donor type or graft source between transplant recipients with and without subsequent thrombosis. In multivariable models, both acute and chronic graft--host disease were independently associated with thrombosis occurrence (Hazard ratio (HR)=2.05, 95% CI 1.52-2.76; HR=1.71, 95% CI 1.19-2.46, respectively). Upper extremity thrombosis differed from all other thromboses in terms of timing, risk factors and clinical impact, and was not associated with non-relapse mortality (HR=1.15; 95% CI 0.69-1.90), unlike all other thromboses which did increase non-relapse mortality (HR=1.71; 95% CI 1.17-2.49). In subgroup analysis evaluating conventional thrombosis predictors by comparing patients with and without thrombosis, a history of prior venous thrombosis was the only significant predictor. Venous thromboembolism has a high incidence after allogeneic stem cell transplant and is associated with graft--host disease and non-relapse mortality.