Incidence of venous thrombosis in a large cohort of 66 329 cancer patients:: results of a record linkage study

Background: The incidence of venous thrombosis (VT) for cancer patients is increased compared with patients without cancer, but estimations of the incidence for different types of cancer have rarely been made because of the low incidence of various types of cancer. Large registries offer an opportunity to study the risk of VT in large cohorts of cancer patients, which is essential in decisions on prophylactic anti-coagulant treatment. Methods: This cohort study estimates the incidence of VT in cancer patients by using record linkage of a Cancer Registry and an Anticoagulation Clinic database in the Netherlands. Cumulative incidences in patients with different types of malignancies were estimated. We calculated relative risks (RRs) in relation to the presence of distant metastases and treatment. Results: Tumors of the bone, ovary, brain, and pancreas are associated with the highest incidence of VT (37.7, 32.6, 32.1, and 22.7/1000/0.5 year). Patients with distant metastases had a 1.9-fold increased risk [RRadj: 1.9; 95% confidence interval (CI): 1.6-2.3]. Chemotherapy leads to a 2.2-fold increased risk (RRadj: 2.2; 95% CI: 1.8-2.7) and hormonal therapy leads to a 1.6-fold increased risk (RRadj: 1.6; 95% CI: 1.3-2.1) compared with patients not using these treatment modalities. Patients with radiotherapy or surgery did not have an increased risk. Conclusions: We compared the overall incidences of VT in the first half year in our study to the risk of major bleeding as described in the literature. For patients with distant metastases, for several types of cancer, prophylactic anti-thrombotic treatment could be beneficial.