Lung cancer, or lung carcinoma, is the uncontrolled division of epithelial cells which line the respiratory tract. There are two main categories of lung cancer: small cell and non-small cell which depend on the type of epithelial cell that’s dividing. Both types can be fatal, especially if the cancerous cells aggressively spread and establish secondary sites of cancer in other tissues. The major cause of lung cancer is smoking tobacco products, and has contributed to the deaths of millions of people, including famous individuals like Walt Disney and Claude Monet.
Now, air enters the respiratory tract through either the nose or mouth, and flows down the trachea, which divides into the right and left bronchi. Each bronchus enters its respective lung at the hilum, or the root of the lung. The bronchi then divides into lobar bronchi, which divide into segmental bronchi, and then into subsegmental bronchi which further branch to form conducting bronchioles, and then respiratory bronchioles which end with small sacs called alveoli that are surrounded by capillaries, which is where gas exchange happens.
Lining these airways are several types of epithelial cells which serve multiple functions. These include ciliated cells that have hairlike projections called cilia that work to sweep foreign particles and pathogens back to the throat to be swallowed. Another type called Goblet cells, which are called that because they look like goblets, secrete mucin to moisten the airways and trap foreign pathogens. There are also basal cells that are thought to be able to differentiate into other cells in the epithelium, club cells that act to protect the bronchiolar epithelium, and neuroendocrine cells that secrete hormones into the blood in response to neuronal signals.
Cells can become mutated because of environmental or genetic factors. A mutated cell becomes cancerous when it starts to divide uncontrollably. As cancer cells start piling up on each other, they become a small tumor mass, and they need to induce blood vessel growth, called angiogenesis, to supply themselves with energy. Malignant tumors are ones that are able to break through the basement membrane. Some of these malignant tumors go a step further and detach from their basement membrane at the primary tumor site, and then enter nearby blood vessels, and establish secondary sites of tumor growth throughout the body—a process called metastasis.