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Lung Cancer Causes

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.
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 increases the risk of lung cancer but not as much as smoking cigarettes.

About 90% of lung cancers arise due to tobacco use. The risk of developing lung cancer is related to the following factors:

the number of cigarettes smoked,
the age at which a person started smoking, and
how long a person has smoked (or had smoked before quitting).

Other causes of lung cancer include the following:

Passive smoking, or secondhand smoke, presents another risk for lung cancer. An estimated 3,000 lung cancer deaths occur each year in the U.S. that are attributable to passive smoking.
Air pollution from motor vehicles, factories, and other sources probably increase the risk for lung cancer, and many experts believe that prolonged exposure to polluted air is similar to prolonged exposure to passive smoking in terms of risk for developing lung cancer.
Asbestos exposure increases the risk of lung cancer by nine times. A combination of asbestos exposure and cigarette smoking raises the risk to as much as 50 times. Another cancer known as mesothelioma (a type of cancer of the pleura or of the lining of the abdominal cavity called the peritoneum) is also strongly associated with exposure to asbestos.
Lung diseases, such as tuberculosis (TB) and chronic obstructive pulmonary disease (COPD), also create a risk for lung cancer. A person with COPD has a four to six times greater risk of lung cancer even when the effect of cigarette smoking is excluded.
Radon exposure poses another risk.
- Radon is a by-product of naturally occurring radium, which is a product of uranium.
- Radon is present in indoor and outdoor air.
- The risk for lung cancer increases with significant long-term exposure to radon, although no one knows the exact risk. An estimated 12% of lung cancer deaths are attributable to radon gas, or 15,000 to 22,000 lung cancer-related deaths annually in the U.S. Radon gas is the second leading cause of lung cancer in the U.S. As with asbestos exposure, smoking greatly increases the risk of lung cancer with radon exposure.
Certain occupations where exposure to arsenic, chromium, nickel, aromatic hydrocarbons, and ethers occurs may increase the risk of lung cancer.
A person who has had lung cancer is more likely to develop a second lung cancer than the average person is to develop a first lung cancer.

Lung Cancer Symptoms

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.

A new cough in a smoker or a former smoker should raise concern for lung cancer.
A cough that does not go away or gets worse over time should be evaluated by a health-care provider.
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.
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.
Repeated respiratory infections, such as bronchitis or pneumonia, can be a sign of lung cancer.

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.

Lung cancer most often spreads to the liver, the adrenal glands, the bones, and the brain.
Metastatic lung cancer in the liver usually does not cause symptoms, at least by the time of diagnosis.
Metastatic lung cancer in the adrenal glands also typically causes no symptoms by the time of diagnosis.
Metastasis to the bones is most common with small cell cancers but also occurs with other lung cancer types. Lung cancer that has metastasized to the bone causes bone pain, usually in the backbone (vertebrae), the thighbones, and the ribs.
Lung cancer that spreads to the brain can cause difficulties with vision, weakness on one side of the body, and/or seizures.

Paraneoplastic syndromes are the remote, indirect effects of cancer not related to direct invasion of an organ by tumor cells. Often they are caused by chemicals released from the cancers. Symptoms include the following:

clubbing of fingers-the depositing of extra tissue under the fingernails
new bone formation-along the lower legs or arms
anemia-low numbers of red blood cells and high calcium level or low sodium level in the blood
other effects-muscle weakness, skin rashes, and degeneration of the brain
weight loss
fatigue
low sodium levels

Lung Cancer Treatment

Treatment decisions in lung cancer depend on whether SCLC or NSCLC is present. Treatment also depends on tumor stage, particularly in NSCLC. A person's general physical condition (the ability to withstand treatment procedures) is also taken into account.

The most widely used therapies for lung cancer are surgery, chemotherapy, and radiation therapy.

Medical Treatment

Chemotherapy and radiation therapy

Chemotherapy and radiation may lead to a cure in a small number of patients. These therapies result in shrinking of the tumor and are known to prolong life for extended periods in most patients.
Chemotherapy and radiation are very effective at relieving symptoms.
Inoperable NSCLCs are treated with chemotherapy or a combination of chemotherapy and radiation.
If SCLC is in an early stage (confined to the thorax), the standard of care is chemotherapy and radiation therapy given at the same time.
In later stages (spread outside of the thorax), SCLC is treated with chemotherapy and palliative radiation therapy to areas where metastases may be present.
The brain is sometimes treated with radiation even if no tumor is present there. Called prophylactic cranial irradiation (PCI), this therapy may prevent a tumor from forming. PCI is not suitable for all patients, however, and side effects may occur.
Limited SCLC (has not spread outside the chest cavity) has an 80%-90% rate of response to combination chemotherapy and radiation therapy. Remission (no cancer detected by physical examination or x-ray studies) occurs in 50%-60% of cases.
Of all cases of advanced-stage lung cancer (spread outside the chest cavity), approximately 50%-60% of SCLC and 15%-40% of NSCLC will go in to remission with chemotherapy.
If relapse occurs, a different type of chemotherapy regimen may offer symptom relief and modest survival benefit.
Even with an initially favorable response to treatment, SCLC tends to relapse within one to two years in most patients, particularly in those with extensive disease.
Recent research has shown benefits of adjuvant chemotherapy in early stage NSCLC in preventing or delaying recurrence of the tumor, even after surgery that is felt to be successful at removing cancer.
Chemotherapy uses chemicals that travel through the bloodstream. It affects both cancerous and healthy cells. This accounts for the many well-known side effects of chemotherapy, including nausea and vomiting, hair loss, skin problems, mouth sores, and fatigue.
Radiation therapy does not affect cells throughout the body the way chemotherapy does. However, it does affect healthy tissues overlying or directly adjacent to the tumor. To a certain extent, the side effects of radiation depend on which part of the body is targeted with radiation.
Based on recent clinical trial data, chemotherapy has been found to be beneficial for all stages of non-small cell lung cancer, including stage I or II. People with lung cancer should be referred to an oncologist for discussion of options.