Comedian and former “Saturday Night Live” cast member Norm MacDonald died Tuesday, after what his brother, Neil MacDonald, described as a nine-year battle with acute leukemia. Norm MacDonald, known for his intelligence and sarcastic wit, was 61. Leukemia is a blood cancer that originates in the blood and bone marrow. It usually occurs when the body creates too many abnormal white blood cells and interferes with the bone marrow’s ability to make red blood cells and platelets, though some leukemias start in other kinds of blood cells. Leukemia accounts for about one-third of all blood cancer diagnoses and was the...