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 > or = 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 > or = 350,000/mm(3) (adjusted OR 2.81, 95% CI 1.63-4.93, P = 0.0002), site of cancer, hemoglobin < 10 g/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.