Cancer Studies > Lung Cancer > Lung Cancer Causes, Symptoms, and Signs

Lung Cancer Overview

Lung cancer is one of the most common cancers in the world. Cigarette smoking causes most lung cancers. Lung cancer is the leading cause of cancer deaths in both women and men in the United States and throughout the world. Lung cancer has surpassed breast cancer as the leading cause of cancer deaths in women. 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. Most lung tumors are malignant.

cancer of lung

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.

Some lung tumors are metastatic from cancers elsewhere in the body. 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.

Lung cancers are usually divided into two main groups that account for about 95% of all cases.

  1. 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).
  2. About 5% of lung cancers are of rare cell types, including carcinoid tumor, lymphoma, and others.
  3. The specific types of primary lung cancers are as follows:
  4. Adenocarcinoma (an NSCLC) is the most common type of lung cancer, making up 30%-40% of all cases.
  5. Squamous cell carcinoma (an NSCLC) is the second most common type of lung cancer, making up about 30% of all lung cancers.
  6. Large cell cancer (another NSCLC) makes up 10% of all cases.
  7. Carcinoid tumors account for 1% of all cases.

Lung Cancer Causes

Cigarette smoking is the most important cause of lung cancer. 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 it is 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 factors of the number of cigarettes smoked,

Other causes of lung cancer include the following:

  1. Passive smoking, or secondhand smoke, presents another risk for lung cancer.
  2. Asbestos exposure increases the risk of lung cancer by nine times.
  3. Lung diseases, such as tuberculosis (TB) and chronic obstructive pulmonary disease (COPD), also create a risk for lung cancer.
  4. Radon exposure poses another risk.

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.

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.

  1. A new cough in a smoker or a former smoker should raise concern for lung cancer.
  2. A cough that does not go away or gets worse over time should be evaluated by a health-care provider.
  3. 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.
  4. 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.
  5. 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.
  6. Wheezing or hoarseness may signal blockage or inflammation in the lungs that may go along with cancer.
  7. 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.

  1. Lung cancer most often spreads to the liver, the adrenal glands, the bones, and the brain.
  2. Metastatic lung cancer in the liver usually does not cause symptoms, at least by the time of diagnosis.
  3. Metastatic lung cancer in the adrenal glands also typically causes no symptoms by the time of diagnosis.
  4. 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.
  5. Lung cancer that spreads to the brain can cause difficulties with vision, weakness on one side of the body, and/or seizures.

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