Lung cancer is the leading cause of cancer deaths worldwide and will account for more than 160,000 deaths in the United States in 2007. It is responsible for more deaths than breast, colon and prostate cancers combined, according to the American Cancer Society (ACS).

Lung cancer is the abnormal growth of malignant cells in the tissues of the lungs and/or airways that grow uncontrollably and destroy healthy cells. This uncontrolled growth may develop over many years and often goes undetected.

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 gases that nourish and cleanse the body’s cells.

A system of small tubes (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 waste product that is sent to the lungs to exhale.

Cancer cells develop because of damaged DNA, which is the genetic blueprint that governs the behavior of cells. In most cases, when the DNA becomes damaged, the body is able to repair it. In cancer cells, however, the DNA is not repaired, which causes the abnormal cells to reproduce more quickly and live longer than normal cells.

Most lung cancers begin in the lining of the bronchi, which is why lung cancer is also known as bronchogenic cancer. Lung cancer spreads quickly and is often not detected until it has metastasized to other areas of the body.

Lung cancer is often thought of as a single disease, but there are two main types: non-small cell lung cancer (NSCLC), which is the most common, and small cell lung cancer (SCLC). The ACS estimates that about 87 percent of lung cancer cases are NSCLC and the remaining 13 percent are SCLC. NSCLC can be divided into subtypes, such as adenocarcinoma, squamous cell carcinoma, and large-cell undifferentiated carcinoma.

Before the 20^th century, when cigarettes were not mass produced or readily available, the disease 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. In areas of the world where more people smoke, there has been a corresponding rise in lung cancer cases.

Lung cancer has declined in the last several years, in conjunction with the decreasing trend in smoking. Although a decine has been found in new cases among men, while the rates for women have remained stable. However, the ACS estimates that there will be about 213,000 new cases of lung cancer in 2007. The disease is typically found in the older population, with nearly 70 percent of the newly diagnosed cases occurring in people over the age of 65.

In general, lung cancer is a particularly deadly form of cancer because most cases are not diagnosed until the disease has metastasized. Death rates following diagnosis have fallen slightly, but they have remained relatively static over the past decade, according to the Centers for Disease Control and Prevention (CDC).

The ACS estimates that almost 60 percent of people diagnosed with lung cancer die within one year of their diagnosis, and nearly 75 percent will die within two years. These rates have not improved over the past 10 years. The overall five-year survival rate for all stages of lung cancer is only 16 percent. Although the chance of survival is typically poor with lung cancer, the ACS estimates that currently there are about 330,000 long-term survivors.