Thrombocytopenia occurs frequently in patients with cancer-associated thrombosis (CAT), however prospective evaluation of clinical outcomes following randomization to anticoagulants is limited. The HOKUSAI VTE Cancer study was a randomized, open-label, non-inferiority, phase III trial comparing dalteparin with edoxaban in CAT patients. This post hoc analysis of Hokusai VTE Cancer Study was performed to compare outcomes in patients with platelet count ≤100 K/μL at one or more specified time points (baseline, 1-month, or 3-month) versus those without thrombocytopenia. Cumulative incidences at 180 days were calculated with death as a competing risk. The primary outcome was major bleeding; secondary outcomes were clinically relevant non-major bleeding (CRNMB), recurrent thrombosis, and survival. The analysis included 1,045 patients with primarily solid tumor malignancies (89%), median age 65 years, and 52% male. The thrombocytopenia group comprised 9.6% (N=101) of the cohort and relative to the non-thrombocytopenia cohort (N=944), experienced significantly higher major bleeding (9.0% vs. 4.0%, sub-distribution hazard ratio (SHR) 2.4, P=0.02) and CRNMB (17.9% vs. 9.6%, SHR 2.0, P=0.01). Thrombocytopenia did not impact recurrent VTE (9.8% vs. 7.4%, SHR 1.3, P=0.37) nor overall mortality (21.8% vs. 26.0%, HR 0.9, P=0.48). Major bleeding was higher in patients with thrombocytopenia and gastrointestinal malignancies receiving edoxaban versus dalteparin (16.8% vs 0, p<0.01) but similar for patients with other malignancies (p=0.30). In patients with hematologic malignances and thrombocytopenia major bleeding was higher for patients received dalteparin compared to edoxaban (19.0% vs. 0, p<0.01). Mild thrombocytopenia was associated with a doubling in risk of major hemorrhage in patients receiving anticoagulation for CAT. Bleeding risk for edoxaban and dalteparin varied in gastrointestinal and hematologic malignances in patients with thrombocytopenia.
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