Chronic lymphocytic leukaemia (CLL) is a condition where you have many abnormal B lymphocyte white blood cells. The lymphocytes look normal under a microscope but are abnormal as they do not function properly. The main reason for the build-up of the abnormal lymphocytes is because they live too long - they do not die after the usual lifespan of a lymphocyte. (This is different to the acute types of leukaemias where the cells rapidly multiply 'out of control'. In CLL the abnormal lymphocytes are not thought to multiply faster than normal lymphocytes.) Typically, CLL progresses very slowly - over months or years, even without treatment.
This is a companion discussion topic for the original article at https://patient.info/cancer/leukaemia/chronic-lymphocytic-leukaemia-cll