The formation of new blood vessels is called angiogenesis. It is a normal part of growth and healing – but it plays a role in several diseases, including cancer. A tumor needs nutrients and oxygen to grow and spread. Blood contains those ingredients. The tumor sends chemical signals that stimulate blood vessel growth. And the blood vessels carry blood to the tumor. Angiogenesis inhibitors, also called anti-angiogenic, are drugs that block angiogenesis. Blocking nutrients and oxygen from a tumor “starves” it. These drugs are an important part of treatment for some types of cancer.