There are three stages of CML: chronic, accelerated and blast. Most people with CML are diagnosed in the chronic stage, where their body makes too many mature white blood cells (called granulocytes).

All cells in your body contain genes (chromosomes) made up of DNA. If you have CML, something goes wrong with how your chromosomes divide and you’ll have what doctors call a ‘Philadelphia chromosome’, an unusual chromosome found inside all of the cancerous cells.