Risk factors for venous thromboembolism in patients treated for differentiated thyroid carcinoma.

Although cancer in general is a strong risk factor for developing venous thromboembolism (VTE), the risk factors for venous thromboembolic events in patients with differentiated thyroid carcinoma (DTC) have never been assessed. This is remarkable, as several parts of the treatment comprise a hypercoagulable state that could in subgroups of DTC patients lead to an increased risk of VTE. The aim of this study was to assess which risk factors could cause DTC patients to develop VTE. We performed a nested case-control study, involving cases of DTC patients treated between 1980 and 2014 with confirmed VTE after diagnosis of DTC. Controls were defined as DTC patients without VTE. In all subjects, we collected information about thyroid cancer characteristics, treatment characteristics, traditional risk factors for VTE and additional clinical data, and we performed univariable and multivariable regression analyses. We included 28 cases and 56 controls matched for age at DTC diagnosis, sex and date of DTC diagnosis. In the univariable regression analysis, histology, distant metastases, DTC risk classification, recent surgery and other active malignancy were associated with VTE. In the multivariable analysis, distant metastases (odds ratio 7.9) and recent surgery (odds ratio 6.1) were independently associated with VTE. In conclusion, surgery and presence of distant metastases are independent risk factors for developing VTE in DTC patients. The risk factors identified in this study could be considered when making decisions regarding thromboprophylaxis for patients with thyroid cancer.