Distant metastases are the principal cause of death from cancer. Many animal experiments in the last 25 years have shown consistently that distant metastases can be significantly reduced by anticoagulants and fibrinolytic agents. Since aspirin inhibits platelet function and increases fibrinolytic activity in humans, it may be effective in preventing metastases in cancer patients. It is suggested that aspirin be offered as an option to cancer patients who are at risk for distant metastases.