Thrombotic antiphospholipid syndrome (TAPS) is characterized by venous, arterial, or microvascular thrombosis. Patients with TAPS merit indefinite anticoagulation, and warfarin has historically been the standard treatment. Apixaban is an oral factor Xa inhibitor anticoagulant that requires no dose adjustment or monitoring. The efficacy and safety of apixaban compared with warfarin for TAPS patients remain unknown. This multicenter prospective randomized open-label blinded endpoint study assigned anticoagulated TAPS patients to apixaban or warfarin (target international normalized ratio 2-3) for 12 months. The primary efficacy outcome was clinically overt thrombosis and vascular death. Apixaban was first given at 2.5 mg twice daily. Two protocol changes were instituted based on recommendations from the data safety monitoring board. After the twenty-fifth patient was randomized, the apixaban dose was increased to 5 mg twice daily, and after the thirtieth patient was randomized, subjects with prior arterial thrombosis were excluded. Primary outcomes were adjudicated by independent experts blinded to treatment allocation. Patients randomized between 23 February 2015 and 7 March 2019 to apixaban (n = 23) or warfarin (n = 25) were similar. Among the components of the primary efficacy outcome, only stroke occurred in 6 of 23 patients randomized to apixaban compared with 0 of 25 patients randomized to warfarin. The study ended prematurely after the forty-eighth patient was enrolled. Conclusions from our study are limited due to protocol modifications and low patient accrual. Despite these limitations, our results suggest that apixaban may not be routinely substituted for warfarin to prevent recurrent thrombosis (especially strokes) among patients with TAPS. This trial was registered at www.clinicaltrials.gov as #NCT02295475.

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Venous thromboembolism (VTE) with concurrent thrombocytopenia is frequently encountered in patients with cancer. Therapeutic anticoagulation in the setting of thrombocytopenia is associated with a high risk of hemorrhage. Retrospective analyses suggest the utility of modified-dose anticoagulation in this population. To assess the incidence of hemorrhage or thrombosis according to anticoagulation strategy, we performed a prospective, multicenter, observational study. Patients with active malignancy, acute VTE, and concurrent thrombocytopenia (platelet count <100 000/µL) were enrolled. The cumulative incidences of hemorrhage or recurrent VTE were determined considering death as a competing risk. Primary outcomes were centrally adjudicated and comparisons made according to initial treatment with full-dose or modified-dose anticoagulation. A total of 121 patients were enrolled at 6 hospitals. Seventy-five patients were initially treated with full-dose anticoagulation (62%) and 33 (27%) with modified-dose anticoagulation; 13 (11%) patients received no anticoagulation. Most patients who received modified-dose anticoagulation had a hematologic malignancy (31 of 33 [94%]) and an acute deep vein thrombosis (28 of 33 [85%]). In patients who initially received full-dose anticoagulation, the cumulative incidence of major hemorrhage at 60 days was 12.8% (95% confidence interval [CI], 4.9-20.8) and 6.6% (95% CI, 2.4-15.7) in those who received modified-dose anticoagulation (Fine-Gray hazard ratio, 2.18; 95% CI, 1.21-3.93). The cumulative incidence of recurrent VTE at 60 days in patients who initially received full-dose anticoagulation was 5.6% (95% CI, 0.2-11) and 0% in patients who received modified-dose anticoagulation. In conclusion, modified-dose anticoagulation appears to be a safe alternative to therapeutic anticoagulation in patients with cancer who develop deep vein thrombosis in the setting of thrombocytopenia.