Leukemias are cancers of the bone marrow (the site of blood cell production). Often the disorder is associated with the overproduction of white blood cells that are immature. Such young white blood cells are not doing as well as they should be. Therefore the patient is often prone to infection. Leukaemia also affects red blood cells and can cause poor blood clotting and Fatigue due to anemia.

Examples of leukemia include:

• Myelogenous or granulocytic leukemia (malignancy of the myeloid and granulocytic white blood cell series)
• Lymphatic, lymphocytic, or lymphoblastic leukemia (malignancy of the lymphoid and lymphocytic blood cell series)
• Polycythemia vera or erythremia (malignancy of various blood cell products, but with red cells predominating)