Increased Incidence of Venous Thromboembolism Following Allogeneic Compared with Autologous Hematopoietic Stem Cell Transplantation.
Authors: Gonsalves Andrew , Carrier Marc , Wells Philip , McDiarmid Sheryl , Huebsch Lothar , Allan David 
Published: October 2019

Abstract
Background: The incidence of venous thromboembolism (VTE) following hematopoietic stem cell transplantation (HSCT) is not well described, particularly with the emerging trend towards increased ambulatory care in the transplant setting. HSCT involves high dose chemotherapy and/or radiation and is often associated with periods of immobilization. In addition, vascular damage and inflammation are common following transplantation and may further increase the risk of VTE. We sought to quantify the incidence of VTE in both allogeneic and autologous HSCT recipients and characterize the factors influencing these events.
Methods: A retrospective analysis involving 589 patients (382 autologous, 207 allogeneic recipients undergoing transplantation between 2000–2005) was performed in order to identify the incidence of symptomatic acute deep proximal vein thrombosis (DVT) or pulmonary embolism (PE) in HSCT recipients. Only patients who provided signed informed consent regarding the utilization of their medical information for research purposes were included. All diagnostic imaging reports of CT pulmonary angiography, ventilation / perfusion (VQ) scanning and duplex ultrasound of the upper and lower extremities performed within the first year after HSCT were reviewed. A diagnosis of VTE was confirmed by reviewing the clinical record and verifying a moderate to high pre-test probability according to the Wells’ criteria. Non-catheter related events were the designated primary outcome. Symptomatic catheter-related events (superficial and deep veins) were secondary outcomes. Statistical analysis included comparison of mean values using Student’s t test and comparison of proportions using the chi squared analysis.
Results: A total of 7 patients developed VTE following HSCT unrelated to central venous catheters (4 PE and 3 DVT) for an incidence of 1.2%. A total of 5 patients had VTE events in the allogeneic group (2.4%) and 2 autologous recipients suffered VTE events (0.52%, p=0.043). An increased number of PEs occurred in the allogeneic group compared with autologous recipients (4 vs 0, p=0.006). Symptomatic catheter-related thrombosis (superficial and deep venous occlusion combined) was not different between the allogeneic and autologous groups (7.25% vs. 5.50%, p= 0.4). Three allogeneic recipients (60%) had GVHD at the time of VTE diagnosis and only 1 patient had relapsing disease (20%) while both patients in the autologous cohort (100%) had progression of their disease at the time of VTE diagnosis. All VTE events unrelated to central venous catheters occurred after hematopoietic engraftment with a trend towards earlier occurrence in the allogeneic setting compared to autologous recipients (mean 153 days vs. 312 days, respectively, p=0.080). The mean platelet count at the time of VTE was 121 (50–174).
Conclusion: HSCT patients have a high incidence of non-catheter related VTE compared to historical reports of the general and cancer populations. Allogeneic recipients have an increased risk of VTE and of PE in comparison to autologous transplant patients. VTE occurred exclusively in HSCT patients after hematopoietic recovery. Perhaps thrombocytopenia and the emphasis on ambulatory patient status in our program were protective against the development of VTE. Our study supports the notion that GVHD may contribute to the development of VTE in allogeneic transplant recipients. Moreover, progression of the underlying malignancy may be a dominant risk factor in the development of VTE in autologous recipients.