Lung cancer is any cancerous growth in lung tissue. The cancers can arise in the lungs, or be metastic (spread) from other sources.

Causes

Lung cancers form in the epithelium (lining) the bronchi ( tubes by which air passes to the lungs), or in the fine air sacs that terminate the passage.
The most common forms originate in bronchial epithelium that has been altered by long exposure to cigarette smoke to form less specialized cells known as squamous cells (flat cells).

The cells that do not become flattened still possibly can become cancerous. The epithelial cells of bronchi may also undergo certain transformations to give rise to adenocarcinomas, but these tumors do not appear to be related to cigarette smoking.

Types

adenocarcinoma - account for some 25 to 30 percent of lung cancers; it is the most common type of lung cancer in the United States. Cells of adenocarcinoma are cube- or column-shaped, and they form structures that resemble glands (hence the name, aden means gland) and are sometimes hollow. Tumors often originate in the smaller, peripheral bronchi; symptoms at the time of diagnosis often reflect invasion of the lymph nodes, pleura, the other lung or the metastasis to other organs.

large-cell carcinomas -20 percent. There is some dispute as to whether it is a distinct type of cancer or merely a group of atypical squamous-cell carcinomas and adenocarcinomas. Large-cell carcinomas generally originate in the peripheral areas of the lung.

small-cell carcinomas - Cancers of this type have tumors that secrete hormones.

Alveolar - The alveoli are small air sacks in the lungs where oxygen is transferred into blood cells. Cancer of the alveoli is any cancer arising in these air sacks

Squamous cell carcinomas - The form differentiation, from specific bronchial epithelium to flattened cells can give rise to cancer, becoming squamous-cell carcinomas. Cancer of this type typically arises on the skin, lips, and throat.

Symptoms

In the earliest stages of lung cancer there are often no symptoms. In later stages symptoms may include coughing, chest pain, shortness of breath, blood in the sputum, and repeated episodes of pneumonia; weight loss, loss of appetite, and weakness may also accompany the disease. Sometimes the first symptoms result from the metastasis of the tumor to other parts of the body.

Cures

The main treatments for lung cancer are surgery, chemotherapy, and radiation. The choice of treatment depends on the patient's general health, the stage or extent of the disease, and the type of cancer. Surgery is the preferred treatment for patients with non-small-cell carcinoma. Many patients, however, have heart or respiratory diseases that limit their ability to tolerate surgery. Surgery is not the main treatment for patients with cancer in both lungs or for those whose cancer has metastasized to distant organs. It is of no value in most cases of small-cell carcinoma; chemotherapy or radiation therapy, or both, are usually used. Small-cell carcinoma responds better to chemotherapy than do other types of lung cancer.

Treatment is most effective in the early stages of the disease, when the tumor is small and the patient is still relatively healthy. Because most patients have extensive lung cancer at the time of diagnosis, however, the outlook is generally poor. A majority of patients die of the disease within one year of its detection, and only some 10 percent survive for five years or more.

Works cited
"respiratory disease" Encyclop├Ždia Britannica Online.
On-line Medical Dictionary . (http://www.graylab.ac.uk/)