Leukaemia blood cells. Light micrograph of blood cells (mainly B cells, dark purple) in the liver of a patient with lymphocytic leukaemia. Leukaemia is a cancer of the white blood cells (leucocytes), and lymphocytic leukaemia affects a particular leucocyte, the lymphocyte, which is responsible for fighting infection. The disease leads to their abnormal proliferation in the bone marrow and by organs of the lymph system, which can result in swollen lymph nodes, fatigue, anaemia and persistent infections.