Inhibitory effects of bortezomib on platelet aggregation in patients with multiple myeloma.

ABSTRACT

INTRODUCTION: Multiple myeloma (MM) therapy affects prothrombotic and anticoagulant processes. Patients receiving thalidomide, especially in combination with steroids, are at increased risk of venous thromboembolism (VTE), while the incidence of VTE on bortezomib is low. In vitro studies indicate that bortezomib causes a reduction in ADP-induced platelet aggregation. OBJECTIVES: To analyse the influence of bortezomib on platelet aggregation induced by various agonists in patients with MM. PATIENTS AND METHODS: A total of 30 patients (median age 57.5years) with relapsed/refractory MM receiving bortezomib-based regimens were analysed. Optical platelet aggregometry was performed with the agonists collagen, ADP and ristocetin and measured over two 21-day cycles. The results from two groups those treated with bortezomib and thalidomide (BT group, n=11) and those without thalidomide (B group, n=19) were analysed. RESULTS: During the second cycle, significantly decreased platelet aggregation was observed in the B group 5µM ADP (p=0.0285, day 1 versus 8); 3.5µM ADP (p=0.0005, day 1 versus 8 and day 1 versus 11), collagen (p=0.0014, day 4 versus 8, day 4 versus 11), 1.25mg/ml ristocetin (p=0.0017, day 1 versus 8 and day 1 versus 11). Agonist-induced platelet aggregation tended to be reduced over time during the 1st cycle in group B. In the thalidomide group, significant platelet aggregation inhibition by collagen only was found. Transient reduction in platelet count was observed in all patients, but more prominently in group B. CONCLUSION: The inhibitory effects of prolonged exposure of bortezomib on platelet aggregation were demonstrated in relapsed/refractory MM patients, but antithrombotic activity of bortezomib should be clarified in further prospective studies.