Plasma Thrombin Generation and Sensitivity to Activated Protein C Among Patients With Myeloma and Monoclonal Gammopathy of Undetermined Significance

The etiology of the prothrombotic state in myeloma has yet to be definitively characterized. Similarly, while recent evidence suggests that patients with monoclonal gammopathy of undetermined significance (MGUS) may also be at increased risk of thrombosis, the magnitude and the etiology of this risk have also yet to be defined. The present study aims to characterize patterns of plasma thrombin generation and sensitivity to the anticoagulant activity of activated protein C (APC) at the time of initial diagnosis of myeloma and in response to therapy in comparison to that observed among patients with MGUS and matched, healthy volunteers. Patients presenting with newly diagnosed/newly relapsed myeloma (n = 8), MGUS (n = 8), and matched healthy volunteers (n = 8) were recruited. Plasma thrombin generation was determined by calibrated automated thrombography. Peak thrombin generation was significantly higher in patients with myeloma (383.4 +/- 33.4 nmol/L) and MGUS (353.4 +/- 16.5 nmol/L) compared to healthy volunteers (276.7 +/- 20.8 nmol/L; P < .05). In the presence of APC, endogenous thrombin potential was significantly lower in control plasma (228.6 +/- 44.5 nmol/L x min) than in either myeloma (866.2 +/- 241.3 nmol/L x min, P = .01) or MGUS plasma (627 +/- 91.5 nmol/L x min, P = .003). Within the myeloma cohort, peak thrombin generation was significantly higher at diagnosis (353.2 +/- 15.9 nmol/L) than following completion of the third cycle of therapy (282.1 +/- 15.2 nmol/L; P < .005). Moreover, sensitivity to APC increased progressively with each cycle of chemotherapy. Further study of the etiology and evolving patterns of hypercoagulability among patients with these conditions is warranted and may have future implications for thromboprophylaxis strategies.