Lung cancer usually occurs because some outside factor, called a carcinogen, has triggered the growth of abnormal, cancerous cells in the lung. These cancerous cells multiply out of control and eventually form a mass called a tumor. As the tumor grows, it destroys nearby areas of the lung. Eventually, the tumor's abnormal cells can spread (metastasize) to nearby lymph nodes and to distant organs, such as the brain. In most cases, the carcinogens that trigger lung cancer are chemicals found in cigarette smoke.

Lung cancers are divided into two basic groups, non–small cell lung cancer and small cell lung cancer, based on the microscopic appearance of the tumor cells. These two groups are treated differently.

Non–Small Cell Lung Cancer

Non–small cell lung cancer is more likely than small cell cancer to be localized at the time of diagnosis. It also is more likely than small cell cancer to be treatable with surgery, but it often responds poorly to chemotherapy. Non–small cell lung cancer is divided into several subgroups based on how the cancerous cells look under a microscope:

• Adenocarcinoma (32% of cases) — This is the most common type of lung cancer. Although it is related to smoking, it is also the most common type of lung cancer seen in nonsmokers. Adenocarcinoma is the most frequent form of lung cancer seen in women and in people younger than 45. It usually develops near the edge of the lung and can involve the membrane covering the lung, called the pleura.



• Squamous cell (epidermoid) carcinoma (30% of cases) — This form of lung cancer tends to develop as an abnormal mass near the center of the lungs. As the mass gets larger, it can bulge into one of the larger air passages, called the bronchi. In 10% to 20% of cases, the tumor forms a cavity in the lungs (cavitates).



• Large cell carcinoma (10% to 20% of cases) — Like adenocarcinoma, large cell carcinoma tends to develop at the edge of the lungs and spread to the pleura. Like squamous (epidermoid) carcinoma, it cavitates in 10% to 20% of patients.



• Adenosquamous carcinoma, undifferentiated carcinoma, and bronchioloalveolar carcinoma — These are three relatively rare forms of non–small cell lung cancer.

Small Cell Lung Cancer

At the time of diagnosis, small cell lung cancer is more likely than non–small cell cancer to have spread beyond the boundaries of the lung. This typically makes it almost impossible to cure with surgery. However, chemotherapy or radiation therapy can be used to manage the cancer. Small cell cancers account for about 20% of all lung cancers.

Risk Factors

About 170,000 people in the United States are diagnosed with lung cancer each year, and the illness is the country's leading cause of cancer deaths. Lung cancer most commonly strikes people between the ages of 55 and 65, and smokers account for 86% to 90% of all cases. Risk factors for lung cancer include:

• Cigarette smoking — Smokers are 13 times more likely to develop lung cancer than nonsmokers. Smoking is a much more significant risk factor for lung cancer than all of the other following risk factors combined.



• Passive cigarette smoking — Nonsmokers who inhale the cigarette fumes of smokers have an increased risk of developing lung cancer. Health experts believe that passive (secondhand) cigarette smoke causes 3,000 lung cancer deaths in nonsmokers each year.



• Exposure to radon gas — Radon is a colorless, odorless radioactive gas that is formed in the ground. It seeps into the lower floors of homes and public buildings, and it also can contaminate drinking water. Radon exposure is the second most important risk factor for lung cancer after smoking. Estimates suggest that it accounts for more than 7,000 lung cancer deaths annually. Elevated radon levels are more likely to contribute to lung cancer in smokers and people exposed to high levels of radon at work, such as miners.



• Exposure to asbestos — Asbestos is a family of fibrous minerals that occur in underground deposits. Asbestos is used in home insulation, fire-proofing, tiles for floors and ceilings, automobile brake linings, and other products. It is believed that irritating asbestos fibers can cause cancer. The risk of lung cancer is higher in workers who are exposed to asbestos on the job (miners, construction workers, auto mechanics who work with brakes), as well as in people who live or work in buildings where asbestos-containing building products are deteriorating. In general, asbestos exposure tends to increase the risk of squamous cell carcinoma or adenocarcinoma, especially in people who also smoke cigarettes.



• Work-related exposure to substances — Substances associated with lung cancer include uranium, arsenic, vinyl chloride, nickel chromates, coal products, mustard gas, chloromethyl ethers, gasoline, diesel exhaust and high levels of talc dust.

In 5% to 15% of cases, a cancerous lung tumor is detected on a routine chest X-ray in a person who doesn't have any symptoms. However, most lung cancer patients have one or more of the following symptoms:

• Cough
• Coughing up blood (hemoptysis)
• Wheezing
• Shortness of breath
• Discomfort during breathing
• Chest pain
• Symptoms of pneumonia (fever and a mucus-producing cough)
• Discomfort during swallowing
• Hoarseness
• Weight loss and poor appetite
• Other symptoms, if cancer has spread to the brain, bones or elsewhere

Your doctor may suspect lung cancer based on your symptoms and your history of smoking. To look for further evidence of cancer, your doctor will examine you, paying special attention to your lungs and chest. Your doctor then will order radiological studies such as chest X-rays and possibly a computed tomography (CT) scan to see any masses better. If cancer is suspected, tests will be done to diagnose the specific type of lung cancer and its extent of spread. These tests may include:

• Sputum sample — In this test, coughed-up mucus is checked in a laboratory for cancer cells.



• Biopsy — In this test, a sample of abnormal lung tissue is removed from the body and taken to a laboratory, where it can be examined under a microscope for signs of cancer. If the biopsy specimen shows cancerous cells, the type of lung cancer can be determined by the way the cells look under the microscope. Although this test often can be done using bronchoscopy, surgery is sometimes necessary to expose the suspicious lung area.



• Bronchoscopy — In this procedure, a tube-like instrument is passed into the lungs through the airways. The goal is to inspect the inside of the lungs directly for cancerous areas and to obtain a biopsy sample.



• Mediastinoscopy — In this procedure, a tube-like instrument is used to biopsy lymph nodes or any masses seen between the lungs (the mediastinum). A biopsy obtained this way can be used to make a diagnosis of the type of lung cancer and check whether the cancer has spread (metastasized) to lymph nodes.



• Fine-needle aspiration — In this procedure, a fine-gauge, sterile needle is guided by CT into a suspicious area of the lungs or pleura. The needle removes a small sample of tissue for laboratory examination.



• Thoracentesis — This procedure is used when lung cancer has caused fluid to accumulate in the chest. This is called a pleural effusion. A sterile needle is used to withdraw a sample of the abnormal fluid for examination in the laboratory.



• Video-assisted thoracoscopic surgery (VATS) — This is a new technique to surgically biopsy abnormal lung tissue on the edges of the lung. It is less invasive than traditional methods of surgery.



• CT scans and bone scans — These scans will check for lung cancer metastases to the brain, liver, bones and elsewhere.

Once it develops, lung cancer will continue to grow and spread until it is treated.

To reduce your risk of lung cancer, you can:

• Avoid cigarette smoking — If you already smoke, ask your doctor about proven ways to help you quit.



• Avoid passive (secondhand) smoke — Choose smoke-free areas of restaurants and hotels. Also, ask house guests to smoke outdoors, especially if there are children in the home.



• Reduce exposure to asbestos — Because there is no safe level of asbestos exposure, any asbestos exposure is too much. Check your home for areas of exposed asbestos-containing insulation or other areas of deteriorating asbestos, especially if you have an older home. These areas must be removed or safely sealed off professionally. If asbestos is not removed properly, you can be exposed to more asbestos than if it was left alone. Workers who deal with asbestos-containing materials routinely should use approved measures to limit their exposure and to keep from bringing asbestos dust home on their clothing.

After lung cancer has been diagnosed, the type of treatment depends on the type of cancer and how much the tumor has spread (the stage).

Non–Small Cell Lung Cancer

Stages of non–small cell lung cancer are categorized by size and how far the tumor has spread. Stages I through III are further divided into "A" and "B" categories.

• Stage I tumors are small and have not invaded the surrounding tissue or organs.
• Stage II and III tumors have invaded surrounding tissue and/or organs and have spread to lymph nodes.
• Stage IV tumors have spread outside the chest area.

Surgery is the primary treatment for early stage (stages I to IIIA) non–small cell lung cancers. Three types of surgery can be done:

• Wedge resection — Only a small part of the lung is removed.
• Lobectomy — One lobe of the lung is removed.
• Pneumonectomy — The entire lung is removed.

Radiation therapy and chemotherapy (the use of strong medications) may be combined with surgery to help prevent cancer from returning.

People with serious medical problems that make it difficult for them to withstand surgery may receive radiation therapy or a combination of radiation and chemotherapy to shrink the tumor.

Lung cancer often is diagnosed at a later stage when it's not possible to remove the tumor surgically. When there is significant tumor spread, chemotherapy may be recommended to slow down cancer growth even if it cannot provide a cure. Chemotherapy has been shown to decrease symptoms and prolong life in advanced cases of lung cancer. Radiation therapy also may be recommended to relieve symptoms.

Small Cell Lung Cancer

The stages for small cell lung cancer are:

• Limited stage — Cancer involves only one lung and its nearby lymph nodes.
• Extensive stage — Cancer has spread outside the lung to other areas of the chest or to distant organs.

The treatment of small cell lung cancer depends on its stage:

• Limited stage — Treatments include various combinations of chemotherapy, radiation and, rarely, surgery, with or without radiation to the brain to prevent cancer spread. While small cell lung cancer often responds well to chemotherapy, it very often returns months to a couple of years later.
• Extensive stage — Treatments include chemotherapy, with or without brain radiation, or radiation treatments to areas of existing metastases in the brain, spine or other bones.

Call your doctor promptly if you have any of the symptoms of lung cancer, especially if you are a smoker or you have worked in an industry with high exposure to asbestos.

The outlook depends on the type of lung cancer, its stage, and the overall health of the patient. In general, only 14% of patients with lung cancer survive for more than 5 years after diagnosis. More specifically, 5-year survival rates vary according to the type of lung cancer:

• Adenocarcinoma — 17%
• Squamous cell carcinoma — 15%
• Large cell carcinoma — 11%
• Small cell carcinoma — 5%

National Cancer Institute (NCI)
U.S. National Institutes of Health
Public Inquiries Office
Building 31, Room 10A03
31 Center Drive, MSC 8322
Bethesda, MD 20892-2580
Phone: (301) 435-3848
Toll-Free: (800) 422-6237
TTY: (800) 332-8615
E-Mail: cancergovstaff@mail.nih.gov
http://www.nci.nih.gov/

American Cancer Society (ACS)
1599 Clifton Road, NE
Atlanta, GA 30329-4251
Toll-Free: (800) 227-2345
http://www.cancer.org/

American Lung Association
61 Broadway, 6th Floor
New York, NY 10006br />Phone: (212) 315-8700
Toll-Free: (800) 548-8252E-Mail: info@lungusa.org
http://www.lungusa.org/

National Heart, Lung, and Blood Institute (NHLBI)
P.O. Box 30105
Bethesda, MD 20824-0105
Phone: (301) 592-8573
TTY: (240) 629-3255
Fax: (301) 592-8563
E-Mail: nhlbiinfo@rover.nhlbi.nih.gov
http://www.nhlbi.nih.gov/

U.S. Environmental Protection Agency (EPA)
Ariel Rios Building
1200 Pennsylvania Ave., N.W.
Washington, DC 20460
Phone: (202) 272-0167
http://www.epa.gov/

National Institute for Occupational Safety and Health
4676 Columbia Parkway
Mail Stop C-18
Cincinnati, OH 45226
Toll-Free: (800) 356-4674
Fax: (513) 533-8573
http://www.cdc.gov/niosh/