When we breathe in, air passes from our nose or mouth through the windpipe (trachea), which divides, into two tubes (airways), one going into each lung. These are known as the right and left bronchus and they divide to form smaller tubes called bronchioles, which carry air through the lungs. At the end of the bronchioles are millions of tiny air sacs or alveoli. It is here that oxygen is absorbed from the air and passes into the bloodstream to be circulated around the body.

The majority of lung cancers develop in the cells which line the right and left bronchus or the bronchioles. Cancers that develop in the lining cells of all organs in the body are called carcinomas. This is why cancers which start in the airways ( bronchus or bronchioles) are called carcinomas but they are more usually referred to as lung cancer.