The medicines – Procrit, Aranesp and Epogen – are multibillion dollar sellers because of their ability to boost oxygen-carrying red blood cells, reducing the need for painful blood transfusions. But sales have fallen sharply since 2007, when the FDA added the first of several safety warnings to the drugs, based on evidence they can cause tumor growth and hasten death in cancer patients. The drugs are no longer used in patients with several types of cancers.