In the United States in 2007, 160,390 people were projected to die from lung cancer, which is more than the number of deaths from colorectal, breast, and prostate cancer combined.

Only about 2% of those diagnosed with lung cancer that has spread to other areas of the body are alive five years after the diagnosis, although the survival rates for lung cancers diagnosed at a very early stage are higher, with approximately 49% surviving for five years or longer.

Some lung tumors are metastatic from cancers elsewhere in the body. The lungs are a common site for metastasis. If this is the case, the cancer is not considered to be lung cancer. For example, if prostate cancer spreads via the bloodstream to the lungs, it is metastatic prostate cancer (a secondary cancer) in the lung and is not called lung cancer.

Cancer occurs when normal cells undergo a transformation that causes them to grow and multiply without the normal controls. The cells form a mass or tumor that differs from the surrounding tissues from which it arises. Tumors are dangerous because they take oxygen, nutrients, and space from healthy cells.

About 90% of lung cancers arise due to tobacco use. Cigarette smoking is the most important cause of lung cancer. Research as far back as the 1950s clearly established this relationship. Cigarette smoke contains more than 4,000 chemicals, many of which have been identified as causing cancer. A person who smokes more than one pack of cigarettes per day has a risk of developing lung cancer 20-25 times greater than someone who has never smoked.

However, Once a person quits smoking, his or her risk for lung cancer gradually decreases. About 15 years after quitting, the risk for lung cancer decreases to the level of someone who never smoked. Cigar and pipe smoking also increases the risk of lung cancer but not as much as smoking cigarettes.

Most lung tumors are malignant. This means that they invade and destroy the healthy tissues around them and can spread throughout the body.

The tumors can also spread to nearby lymph nodes or through the bloodstream to other organs. This process is called metastasis. When lung cancer metastasizes, the tumor in the lung is called the primary tumor, and the tumors in other parts of the body are called secondary tumors or metastatic tumors.

Adenocarcinoma (an NSCLC) is the most common type of lung cancer, making up 30%-40% of all cases. A subtype of adenocarcinoma is called bronchoalveolar cell carcinoma, which creates a pneumonia-like appearance on chest x-rays. Squamous cell carcinoma (an NSCLC) is the second most common type of lung cancer, making up about 30% of all lung cancers. Large cell cancer (another NSCLC) makes up 10% of all cases. SCLC makes up 20% of all cases. And finally, Carcinoid tumors account for only 1% of all cases.

Lung cancers are usually divided into two main groups that account for about 95% of all cases. These division into groups is based on the type of cells that make up the cancer. About 5% of lung cancers are of rare cell types, including carcinoid tumor, lymphoma, and others.

The two main types of lung cancer are characterized by the cell size of the tumor when viewed under the microscope. They are called small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC). NSCLC includes several subtypes of tumors. SCLCs are less common, but they grow more quickly and are more likely to metastasize than NSCLCs. Often, SCLCs have already spread to other parts of the body when the cancer is diagnosed.

Up to one-fourth of all people with lung cancer may have no symptoms when the cancer is diagnosed. These cancers usually are identified incidentally when a chest x-ray is performed for another reason. The majority of people, however, develop symptoms. The symptoms are due to direct effects of the primary tumor, to effects of metastatic tumors in other parts of the body, or to disturbances of hormones, blood, or other systems caused by the cancer.

Symptoms of primary lung cancers include cough, coughing up blood, chest pain, and shortness of breath. Symptoms of metastatic lung tumors depend on the location and size. About 30%-40% of people with lung cancer have some symptoms or signs of metastatic disease.

A cough that does not go away or gets worse over time should be evaluated by a health-care provider. Also, Coughing up blood (hemoptysis) occurs in a significant number of people who have lung cancer. Any amount of coughed-up blood is cause for concern. Chest pain is a symptom in about one-fourth of people with lung cancer. The pain is dull, aching, and persistent and may involve other structures surrounding the lung.

Additionally, shortness of breath usually results from a blockage to the flow of air in part of the lung, collection of fluid around the lung (pleural effusion), or the spread of tumor throughout the lungs. Wheezing or hoarseness may signal blockage or inflammation in the lungs that may go along with cancer. Finally, Repeated respiratory infections, such as bronchitis or pneumonia, can be a sign of lung cancer.