An antineoplastic effect of anticoagulant agents has often been suggested. Heparin and vitamin K antagonists have both been tested in this context. Heparin has been more extensively studied. Data from clinical trials of thromboprophylaxis in cancer patients have suggested that heparin may have beneficial effects on survival in these patients, with a major role for low-molecular-weight heparin compared with unfractionated heparin. Recently, the results of new prospective randomized clinical trials to evaluate the effect of low-molecular-weight heparin on cancer survival have become available. The published data look promising and provide an important step forward in the research knowledge in this field.