Circulating procoagulant microparticles in cancer patients.

Accumulating evidence indicates that microparticles (MPs) are important mediators of the interaction between cancer and the hemostatic system. We conducted a large prospective cohort study to determine whether the number of circulating procoagulant MPs is elevated in cancer patients and whether the elevated MP levels are predictive of occurrence of venous thrombembolism (VTE). We analyzed plasma samples of 728 cancer patients from the ongoing prospective observational Vienna Cancer and Thrombosis Study. Study endpoint was the occurrence of symptomatic VTE. Sixty-five age- and sex-matched healthy controls were recruited for defining the cut-off point for elevated MPs (4.62 nanomolar phosphatidylserine [nM PS]), which was set at the 95th percentile of MP levels in healthy controls. The measurement of MPs was performed after capture onto immobilized annexin V, and determination of their procoagulant activity was quantified with a prothrombinase assay. During a median observation period of 710 days, 53 patients developed VTE. MP levels (nM PS) were significantly higher in cancer patients than in healthy controls (median [25th-75th percentile], 3.95 [1.74-7.96] vs. 1.19 [0.81-1.67], p<0.001). Multivariate analysis including age, sex, surgery, chemo- and radiotherapy showed no statistically significant association of the hazard ratio of elevated MPs with VTE (0.95 [95% CI, 0.55-1.64], p=0.856). In conclusion, MP levels were elevated in cancer patients compared to healthy individuals in this study. However, elevated MP levels were not predictive of VTE.