Lung cancer forms a major problem in our present time. In the US alone it accounts for more than 100,000 deaths every year. The cause of lung cancer varies. The most common cause of lung cancer is cigarette smoking. Another cause is exposure to industrial chemical compounds which lead in many cases to cancer of the lung.
The mechanism of how smoking causes cancer is not certain, because smoke has many compounds which can be carcinogenic such as polycyclic aromatic hydrocarbons in addition to aromatic amines and heavy metals such as nickel. Any of these compounds can be a potential for a carcinogenic material.
The smoking itself produces a change in the epithelium that lines the lung surface from the inside. This process is called metaplasia. Chronic smoking leads to metaplasia or a change in the epithelium of the lung from columnar epithelium to squamous epithelium. There is as a result impaired ciliary movement of the epitheium villi which leads to impaired mechanism of mucus expulsion from the bronchus. Metaplasia itself is not premalignant but its transformation into a dysplastic tissue can be premalignant.
The smoking process is strongly associated with squamous cancer of the lungs. In addition small cell undifferentiated carcinoma of the lung is also associated with smoking but less so than adenocarcinoma. Industrial material can also be carcinogenic which can predispose to lung cancer. Especially noticeable is asbestos as a cause of lung cancer. Metals in addition to other compounds that are found in mines such as uranium and nickel are also associated with carcinogenicity.
Exposure to X-ray radiation as occurs in cancer radiotherapy is itself carcinogenic due to its ionizing power. In addition radioactive radiation is also associated with increased incidence for development of cancer.
The classification of types of lung cancer according to the international classification of lung carcinoma by the world heath organization is divided into four types. The first of which is the squamous carcinoma of the lung eoithelium. It arises in metaplastic squamous epithelium of the bronchi.
This type of lung cancer is strongly associated with cigarette smoking. It accounts for more than 40% of all lung cancer types. This type of cancer tends to be localized forming large masses in the lung. Adenocarcinoma of the lung is the second type of lung cancer. It is involved in the formation of glands that secrete mucin by the malignant cells. This type of cancer accouts for more than 10% of of all lung cancer and is also associated with cigarette smoking but not as much as squamous carcinoma.
Small cell lung carcinoma or oat cell is the third type of lung cancer. It accounts for more than 10% of all lung cancer and is strongly associated with smoking. They usually arise in the large bronchi. The last type of lung cancer that is discussed here is the large cell lung carcinoma of the lungs. It accounts for less than 20 percent but more than five percent of all cases of lung cancer.