C0065 White blood cell count measured prior to cancer development is associated with future risk of venous thromboembolism in cancer patients' the Tromsø study

Abstract

Background: Leukocytosis is an independent risk factor for mortality in cancer patients. Elevated white blood cell (WBC) count, and neutrophils in particular, is also associated with increased risk of venous thromboembolism (VTE) in patients with manifest cancer initiating chemotherapy. It is not known whether the risk of VTE by WBC in cancer patients is causal or merely a consequence of the disease. To address this question we studied the association between WBC count, measured prior to cancer development, and risk of VTE in subjects without and with development of cancer during follow-up in a prospective population-based study. Methods: Baseline characteristics, including total WBC and neutrophil counts, were measured in 24463 initially cancer-free subjects who participated in the Tromso study in 1994–1995. Cancer diagnosed at least one year after WBC measurements and incident venous thromboembolism occurring after the cancer diagnoses were registered up to September 1st, 2007. Cox-regression models were used to calculate hazard ratios (HR) with 95% confidence interval (CI) for VTE. Results: There were 1647 subjects who developed cancer and 353 incident VTE events, ofwhich 84 (24%) occurred in the cancer-group (15.6 per 1000 person-years) and 269 (76%) in the cancer-free group (1.15 per 1000person-years) during follow-up. The risk of VTE increased by 29%per one standard deviation (1SD=2.38×109 cells/L) increase in total WBC (multivariable HR 1.29; 95% CI 1.14–1.46) among cancer patients. WBC count≥8.5×109 cells/L was associated with a 2-fold higher adjusted risk of VTE compared to WBC countb6.5×109 cells/L (HR 2.0, 95% CI 1.163.72). Similar findings were observed for neutrophils. No association was found betweenWBC count and VTE in cancer-free subjects. Comment: Total WBC and neutrophil counts measured prior to cancer development were associated with risk of VTE in cancer patients, but not in cancer-free subjects. Our findings suggest that neutrophils may play a causative role inVTE among cancer patients rather thanonly reflecting the low-grade inflammation associated with cancer.