Immune checkpoint inhibitors for cancer and venous thromboembolic events

Immune checkpoint inhibitors (ICIs) are widely used cancer treatments. There are limited data on the risk for developing venous thromboembolism (VTE) among patients on an ICI.

This was a retrospective study of 2854 patients who received ICIs at a single academic centre. VTE events, defined as a composite of deep vein thrombosis or pulmonary embolism, were identified by individual chart review and blindly adjudicated using standard imaging criteria. A self-controlled risk-interval design was applied with an 'at-risk period' defined as the two-year period after and the 'control period', defined as the two-year before treatment. The hazard ratio (HR) was calculated using a fixed-effect proportional hazards model.

Of the 2854 patients, 1640 (57.5%) were men; the mean age was 64 ± 13 years. The risk for VTE was 7.4% at 6 months and 13.8% at 1 year after starting an ICI. The rate of VTE was > 4-fold higher after starting an ICI (HR 4.98, 95% CI 3.65-8.59, p < 0.001). There was a 5.7-fold higher risk for deep vein thrombosis (HR 5.70, 95% CI 3.79-8.59, p < 0.001) and a 4.75-fold higher risk for pulmonary embolism (HR 4.75, 95% CI 3.20-7.10, p < 0.001). Comparing patients with and without a VTE event, a history of melanoma and older age predicted lower risk of VTE, while a higher Khorana risk score, history of hypertension and history of VTE predicted higher risk.

The rate of VTE among patients on an ICI is high and increases after starting an ICI.