This chronic type of cancer has a slow course and may take years to advance. Myeloid means that the type of abnormal blood cell overproduced by the body is a white blood cell called a myeloid cell. Thus chronic myeloid leukaemia is a slow-developing cancer. CML usually originates in the spinal cord.

CML has three phases: chronic phase, acceleration phase and acute phase or blast crisis. Moving from one phase to another, the cancer develops and symptoms become stronger.

The morbidity of chronic myeloid leukaemia is 1.5 cases per 100,000 people per year. Most new cases occur in those aged 60-80, with men becoming ill more often than women.