Malignancy is an acquired thrombophilic condition that significantly increases the risk of thrombosis. Both venous and arterial thromboembolisms are recognized complications in patients with cancer. In addition, clotting activation may have a role in tumor progression. The pathogenesis of thrombophilia in cancer is multifactorial; however, an important role is attributed to the tumor cell capacity to interact with and activate the host hemostatic system. Recently, new strategies to prevent and cure thrombosis in cancer have become available, thus improving the management of thrombotic complications in the malignant disease. An antineoplastic effect of anticoagulant agents has also been suggested. Both heparins and vitamin K antagonists have been tested in this context. Heparins have been more extensively studied. Recently, the results of prospective, randomized clinical trials to evaluate the effect of low-molecular-weight heparin on cancer survival have created new interest in this area. The published data are promising and provide new information in the research knowledge in this field. The potential anticancer activity of heparins is supported by data from in vitro and experimental studies.