1. ¹The Department of Clinical Epidemiology, Aarhus University Hospital, Ole Worms Allé 150, 8000 Aarhus C, Denmark
2. ²The Danish Cancer Society, Institute of Cancer Epidemiology, Strandboulevarden 49, 2100 Copenhagen Ø, Denmark
3. ³Departments of Medicine and Community and Family Medicine, Dartmouth Medical School, Hanover, NH 03755-3861, USA

Correspondence: Professor HT Sørensen, E-mail: hts@dce.au.dk

Received 3 May 2005; Revised 27 June 2005; Accepted 1 August 2005; Published online 30 August 2005.

Abstract

Although venous thromboembolism (VTE) is common in patients with cancer, it is not known if it is associated with risk of a second malignancy. Using the Danish Cancer Registry and National Registry of Patients, we studied a population-based cohort of 6285 patients with cancer who had an episode of VTE. The risk of a second cancer was compared with that among 30 713 cancer patients without VTE, matched for age, sex, cancer site and year of diagnosis. Overall, the relative risk for a second cancer diagnosis was 1.3 (95% confidence interval (CI) 1.1–1.4). However, the excess risk varied with the time from the initial cancer diagnosis to the thrombotic event. If the thrombotic episode occurred within the first year, the relative risk for a second cancer was 1.0 (95% CI 0.9–1.3), but if the VTE occurred more than 1 year after the initial cancer, the overall relative risk for a second cancer was 1.4 (95% CI 1.2–1.7), with strong associations for cancers of the digestive organs, ovary and prostate. The association between VTE and subsequent incident cancer extends to patients who already have had a cancer diagnosis.