The findings of a study published in Blood suggest that patients treated for cancer with immune checkpoint inhibitor therapy may show an increased risk of thromboembolism, particularly venous thromboembolism (VTE).

Patients in this retrospective cohort study were identified from pharmacy records obtained through the Medical University of Vienna in Austria, and they received immune checkpoint inhibitor therapy for cancer within the years of 2015 through 2018. The researchers conducting the study evaluated patient records for occurrences of VTE and of arterial thromboembolism (ATE), as well as outcomes and possible risk factors.

A total of 672 patients were included in the analysis, with a median age of 64 years at the start of therapy. A total of 47 VTEs and 9 ATEs were reported by a median follow-up of 8.5 months. During immune checkpoint inhibitor therapy, the cumulative incidence of VTE was 12.9% (95% CI, 8.2-18.5%). Cumulative incidence at 24 months was 9.0% (95% CI, 6.4-12.1%) for VTE and 1.8% (95% CI, 0.7-3.6%) for ATE. VTEs typically consisted of pulmonary embolism (PE) and deep vein thrombosis, while observed ATEs included acute coronary syndrome, ischemic stroke, and acute vascular occlusion.

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At a median follow-up for survival analysis of 23.1 months, the median overall survival was 25.4 months (95% CI, 21.0-38.6). The median progression-free survival was 6.2 months (95% CI, 5.1-7.4). VTE in this study was linked to mortality, with a transition hazard ratio of 3.09 (95% CI, 2.07-4.60). A fatal PE was reported in 1 patient and another patient died in a circumstance of clinical suspicion of PE. A fatal ATE event of ischemic stroke occurred in another patient.

VTE history was linked to VTE risk (subdistribution hazard ratio [SHR], 3.69 [95% CI, 2.00-6.81]), and VTE risk appeared to have a nonsignificant association with metastatic disease (SHR, 1.71 [95% CI, 0.62-4.73]). Multiple potential risk factors that were examined did not show significant links to VTE risk. VTE risk also seemed similar across commonly used immune checkpoint inhibitor agents, programmed death-ligand 1 expression levels on tumor cells, and most tumor types. However, patients with gynecological cancer appeared to have an elevated VTE risk (SHR, 4.08 [95% CI, 1.43-11.63]).

“The cumulative incidence estimates of our analysis indicate that approximately every 10th patient experiences VTE during immune checkpoint inhibitor therapy and every 50th patient suffers an ATE,” wrote the researchers in their report. They concluded that more research is needed to characterize VTE or ATE risk in patients receiving this type of therapy.

Disclosures: Some authors have declared affiliations with or received grant support from the pharmaceutical industry. Please refer to the original study for a full list of disclosures.


Moik F, Chan WSE, Wiedemann S, et al. Incidence, risk factors, and outcomes of venous and arterial thromboembolism in immune checkpoint inhibitor therapy. Blood. 2021;137(12):1669-1678. doi:10.1182/blood.2020007878

This article originally appeared on Hematology Advisor