Aplastic anemia (AA) is a severe hematologic condition in which the body fails to make blood cells in sufficient numbers. Aplastic anemia is associated with cancer and various cancer syndromes. Blood cells are produced in the bone marrow by stem cells that reside there. Aplastic anemia causes a deficiency of all blood cell types: red blood cells, white blood cells, and platelets. It occurs most frequently in people in their teens and twenties but is also common among the elderly. It can be caused by heredity, immune disease, or exposure to chemicals, drugs, or radiation. However, in about half of cases, the cause is unknown. Aplastic anemia can be definitively diagnosed by bone marrow biopsy. Normal bone marrow has 30¨C70% blood stem cells, but in aplastic anemia, these cells are mostly gone and are replaced by fat. First-line treatment for aplastic anemia consists of immunosuppressive drugs¡ªtypically either anti-lymphocyte globulin or anti-thymocyte globulin¡ªcombined with corticosteroids, chemotherapy, and ciclosporin. Hematopoietic stem cell transplantation is also used, especially for patients under 30 years of age with a related, matched marrow donor. Aplastic anemia is known to have caused the deaths of Marie Curie, Eleanor Roosevelt, Luana Reyes, and Molly Holzschlag.

Reference
Wiki: Aplastic anemia