Which patients with unprovoked VTE should receive extended anticoagulation? the minority.

Venous thromboembolism (VTE) is associated with a long term risk of recurrence. This risk is at least in part related to the presence of major identifiable risk factors at the time of the index event. It is generally low in the presence of removable risk factors, and very high in the presence of permanent risk factors such as active cancer. This categorization is important because it drives the duration of secondary prevention treatment with anticoagulant drugs. Unfortunately, up to 40-50% of VTE events remain classified as unprovoked. This large group of patients is obviously heterogeneous, with an unpredictable risk of recurrence. Evidences from clinical trials suggest that extending secondary prevention with vitamin K antagonists (VKAs) for 1 or 2 years after an initial course of treatment in patients with unprovoked VTE does not provide additional benefit in terms of reducing the long term risk of recurrence. Prolonging indefinitely the duration of treatment would likely be effective in reducing this risk, but at the cost of unnecessarily expose the majority of patients to several complications, there including major bleeding events, and inconveniences. A number of variables have been identified to predict the individual risk of recurrence in these patients and some clinical prediction rules have been proposed. Improved patients stratification, together with a better understanding of the mechanisms underlying unprovoked VTE, should allow physicians to individually tailor the optimal duration of secondary prevention and to identify those patients (likely the minority) for whom indefinite duration of treatment is warranted.