Lung cancer is often thought of as a single disease, but it is commonly divided into two main types: non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC). NSCLC is by far the most common form, accounting for about 87 percent of lung cancer cases. NSCLC is generally less aggressive than SCLC. SCLC may initially respond more rapidly and dramatically to treatment, but stage for stage, the survival rates are poorer than NSCLC.

Lung cancer is the abnormal growth of malignant cells in the tissues of the lungs or airways. Cancer cells develop because of damage to DNA, the genetic blueprint present in every cell. The body usually can repair damage to DNA. In cancer cells, however, the DNA is not repaired and the abnormal cells reproduce quickly and often live longer than normal cells.

The lungs are sponge-like, cone-shaped organs located in the chest cavity. The left lung has three lobes and the right has two lobes. The lungs are part of the respiratory system and are responsible for the healthy exchange of oxygen and carbon dioxide necessary for the functioning of the body’s cells. A system of small (bronchioles) and larger tubes (bronchi) carry air to and from the lungs for processing in air sacs called alveoli. The oxygen is carried through the bloodstream and made available to the cells in the body. The bloodstream also picks up the carbon dioxide from the cells, a metabolic waste product that is sent to the lungs to exhale.

NSCLC can begin in different regions of the lung. The most common type usually begins in the bronchi, which is the reason it is often called bronchogenic cancer. Although NSCLC is more likely than SCLC to be found early, it still can metastasize (spread) quickly. It can spread through the lymphatic system and bloodstream and by direct invasion of all surrounding structures.

The American Cancer Society (ACS) estimates there will be more than 213,000 new cases of lung cancer in 2007, of which 87 percent will be NSCLC. Lung cancer is the leading cause of cancer deaths with an estimated 161,000 in 2007. The one-year survival rate for both types of lung cancer has increased since the 1970s to approximately 40 percent. However, only about 16 percent of individuals diagnosed with lung cancer live for five years or more after initial diagnosis. Prognosis depends on:

• Stage of the cancer
• Type of cancer cell
• Presence of symptoms
• Patient’s overall health
  

Before the 20^th century, when cigarettes were not mass produced or readily available, lung cancer in general was rarely seen. As cigarettes became widely available, cases of lung cancer rose dramatically. Today, smoking is responsible for about 87 percent of lung cancer cases, according to the ACS. The connection between cigarettes and lung cancer is overwhelming. Wherever smoking is on the increase in the world, there is a corresponding rise in lung cancer cases.

Lung cancer primarily occurs in older people, with 75 percent of the cases diagnosed in people over age 65. Other risk factors for lung cancer include exposure to radon gas, asbestos and other environmental agents. Despite the high mortality associated with lung cancer, the ACS estimates there are currently 330,000 long-term survivors in the United States.