Risk factors for chemotherapy-associated venous thromboembolism in a prospective observational study

BACKGROUND. The incidence of venous thromboembolism (VTE) is increased in cancer, but little information is available about risk factors in cancer patients on chemotherapy. METHODS. We analyzed data from a prospective, multicenter observational study to determine the frequency and risk factors for VTE in ambulatory cancer patients initiating a new chemotherapy regimen. The association of VTE with clinical variables was characterized using univariate and multivariate analysis. RESULTS. Among 3003 patients treated with at least one cycle of chemotherapy, VTE occurred in 58 (1.93%) over a median follow-up of 2.4 months (0.8%/mo). The incidence varied significantly by site of cancer (P = 0.01) with highest rates in upper gastrointestinal (2.3%/mo) and lung cancer (1.2%/mo), and lymphoma (1.1%/mo). An elevated prechemotherapy platelet count was significantly associated with an increased rate of VTE (P for trend = 0.005). The incidence of VTE was 3.98% (1.66%/mo) for patients with a prechemotherapy platelet count >= 350,000, compared with 1.25% (0.52%/mo) for patients with platelet counts of < 200,000 (P for trend=0.0003). In multivariate analysis, a prechemotherapy platelet count of >= 350,000/mm(3) (adjusted OR 2.81, 95% CI 1.63-4.93, P = 0.0002), site of cancer, hemoglobin < 10g/dL or use of erythropoietin, and use of white cell growth factors in high-risk sites of cancer were significantly associated with VTE. CONCLUSIONS. Symptomatic VTE is a frequent complication of chemotherapy. The prechemotherapy platelet count is a unique risk factor and can help identify high-risk patients for future trials of thromboprophylaxis.