When you breathe in, air passes from your nose or mouth through the windpipe (trachea), which divides into two tubes (airways), one going to each lung.These are referred to as the right and left bronchus, which split to create smaller tubes known as bronchioles that transport air through the lungs. Millions of small air sacs called alveoli are found at the end of the bronchioles. The oxygen in the air we breathe in is taken up by the alveoli and transported to the bloodstream where it is distributed throughout the body.

Carbon dioxide is a waste gas that must be removed from the body. It passes from the bloodstream into the alveoli and is then breathed out by the lungs.

The left lung has two major regions (referred to as lobes) whereas the right lung has three.

The term "carcinomas of the bronchus" refers to several lung cancers that develop from cells lining the bronchi.

Non-small cell lung cancer stages

• Stage I: At this point, the cancer has infiltrated the lung tissue underneath but has not yet spread to the lymph nodes.
• Stage II: At this point, the cancer has either infiltrated the chest wall or spread to nearby lymph nodes.
• Stage IIIA: At this point, the cancer has moved from the lung to the chest's lymph nodes.
• Stage IIIB: The cancer has progressed locally to structures including the heart, blood vessels, trachea, and esophagus, all of which are located in the chest, as well as to lymph nodes around the collarbone and the pleura, the membrane that covers the lungs inside the rib cage.
• Stage IV: The cancer has progressed to the liver, bones, or brain, among other organs.

Stages of small cell lung cancer

• Limited. cancer is confined to one lung and to its neighboring lymph nodes.
• Extensive.cancer has spread beyond one lung and nearby lymph nodes, and may have invaded both lungs, more remote lymph nodes or other organs.