Patient with Blood Clot in Leg (IMAGE) The Ottawa Hospital Caption Blood clots in the legs can cause swelling, redness and pain. If a clot forms in the lungs, it can be deadly. New research provides the first approach for safely preventing these clots in people with cancer. Credit The Ottawa Hospital Usage Restrictions Only for use in stories about this research. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.