Illustration of chronic myeloid leukaemia. Seen passing in the interior of this branching blood vessel, between red blood cells, are myeloblast cells in large numbers that establish this type of blood cancer. Myeloblasts (here, coloured pink with white border) are immature white blood cells that proliferate uncontrollably. The causes of chronic myeloid leukaemia are unknown. Two phases normally occur: a chronic phase that may last some years; and a more malignant, acute phase. Symptoms of the first phase include tiredness, fever, loss of weight, and are sometimes not apparent until a blood test is taken. Treatment includes anticancer drugs, and a bone marrow transplant.