Purpose: Despite the strong association between malignant disease and thromboembolic disorders, the molecular and cellular basis of this relationship remains uncertain. We evaluated the hypothesis that tumor-derived tissue factorbearing microparticles in plasma contribute to cancer-associated thrombosis.

Experimental Design: We developed impedance-based flow cytometry to detect, quantitate, and size microparticles in platelet-poor plasma. We evaluated the number of tissue factorbearing microparticles in a cohort of cancer patients of different histologies (N = 96) and conducted a case-control study of 30 cancer patients diagnosed with an acute venous thromboembolic event (VTE) compared with 60 cancer patients of similar age, stage, sex, and diagnosis without known VTE, as well as 22 patients with an idiopathic VTE.

Results: Tissue factorbearing microparticles were detected in patients with advanced malignancy, including two thirds of patients with pancreatic carcinoma. Elevated levels of tissue factorbearing microparticles were associated VTE in cancer patients (adjusted odds ratio, 3.72; 95 confidence interval, 1.18-11.76; P = 0.01). In cancer patients without VTE, a retrospective analysis revealed a 1-year cumulative incidence of VTE of 34.8 in patients with tissue factorbearing microparticles versus 0 in those without detectable tissue factorbearing microparticles (Gray test P = 0.002).The median number of tissue factorbearing microparticles in the cancer VTE cohort (7.1 10⁴ microparticles/L) was significantly greater than both the idiopathic VTE and cancerno VTE groups (P = 0.002 and P = 0.03, respectively). Pancreatectomy in three patients eliminated or nearly eliminated these microparticles which coexpressed the epithelial tumor antigen, MUC-1.

Conclusion: We conclude that tumor-derived tissue factorbearing microparticles are associated with VTE in cancer patients and may be central to the pathogenesis of cancer-associated thrombosis. (Clin Cancer Res 2009;15(22):683040)