Close-up of lung cancer cell division, coloured scanning electron micrograph (SEM). The cells are at the point of division (cytokinesis) where the parent cells will divide into two daughter cells. Lung cancer occurs when abnormal cells divide in a chaotic and uncontrolled manner resulting in the formation of a tumour in the lungs. Lung cancer is the most common cause of cancer death in the UK. In 2016 it accounted for 21% of all cancer deaths in the UK. In terms of survival, approximately 5% will survive 10 years or more and 10% will survive 5 years or more. Magnification: x19000 when printed at 10cm wide.