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Lung cancer

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Epidemiology (Occurance of lung cancer in different groups)

At the end of the 20th century, lung cancer had become one of the world’s leading causes of preventable death.1 Lung cancer is the cancer that forms in tissues of the lung, usually in the cells lining the air passages. In USA, lung cancer remains the leading cause of cancer death in both men and women. The most important cause of lung cancer is exposure to tobacco smoke through active or passive smoking. The reductions in smoking prevalence in men that occurred in the late 1960s through the 1980s will continue to drive the lung cancer mortality rates downward in men during the first portion of this century.2

Types of lung cancer

Lung cancer could be either primary or secondary.

Primary lung cancer: Cancer that has started in the lungs  

Secondary lung cancer: Cancer that has spread to the lungs

Primary lung cancer is mainly of two types:

  • Small cell lung cancer
  • Non-small cell lung cancer

Small Cell Lung Cancer

This type of lung cancer constitutes about 20% of all lung cancers. Small cell lung cancer is so called because the cancer cells are small cells that are mostly filled with the nucleus. This is almost always caused by smoking. It is very rare in nonsmokers. It often spreads in the early stages itself.

Non-Small Cell Lung Cancer

There are three types of non-small cell lung cancer. They behave in a similar way and respond to treatment differently to small cell lung cancer. These three types are:

  • Squamous cell carcinoma
  • Adenocarcinoma
  • Large cell carcinoma

Occasionally, it might not be possible to decipher the type of non-small cell lung cancer. Then, it is called as undifferentiated non-small cell lung cancer. This will not make any difference to the treatment as all non-small cell lung cancers are treated the same way at present.

Signs and Symptoms of lung cancer

Lung cancer typically doesn’t cause signs and symptoms in its earliest stages. Signs and symptoms of lung cancer typically occur only when the disease is advanced.

Signs and symptoms of lung cancer may include:

Other symptoms that are associated with lung cancer include:

  • Weakness
  • Chills
  • Swallowing difficulties
  • Speech difficulties or changes (e.g., hoarseness)
  • Finger/nail abnormalities (e.g., ‘clubbing,’ or overgrowth of the fingertip tissue)
  • Skin paleness or bluish discoloration
  • Muscle contractions or atrophy (shrinkage)
  • Joint pain or swelling
  • Facial swelling or paralysis
  • Eyelid drooping
  • Bone pain/tenderness
  • Breast development in men

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Risk Factors for lung cancer

Researches have found several risk factors for lung cancer. A ‘risk factor’ is anything that changes risk of getting a disease. Different risk factors change risk by different amounts.

The risk factors for lung cancer include the following:

Smoking (both active and passive): People who smoke are 10–20 times more likely to get lung cancer or die from lung cancer than people who do not smoke. The longer a person smokes and the more cigarettes smoked each day the more risk goes up.3–6

Things around us: at home or work place (such as radon gas): Several things may cause cancer (carcinogens) at the workplace or even at the home. For example, radon gas causes lung cancer and is sometimes found in people’s homes. Radon is an odorless, colorless gas that comes from rocks and dirt and can get trapped in houses and buildings. Examples of substances found at some workplaces that increase risk include asbestos, arsenic, and some forms of silica and chromium. For many of these substances, the risk of getting lung cancer is even higher for those who also smoke.4,5

Personal traits (such as having a family history of lung cancer): Risk of lung cancer may be higher if a person’s parents, siblings (brother or sister), or children have had lung cancer.

Diagnosis of Lung cancer

Physical Examination: Patients who are suspected of having lung cancer should undergo a thorough physical examination. In addition, the following tests are performed to diagnose lung cancer.

Sputum examination is done to check if the sputum contains bacteria, other infectious organisms or cancer cells. If sputum analysis does not provide a definite diagnosis, more tests are warranted.

Chest radiograph is used to detect enlarged lymph nodes in the chest or a localized mass in the lungs.

Computed tomography (CT or ‘CT’ scan) is a computer-assisted technique that produces cross-sectional images of the body.

Magnetic resonance imaging (MRI scan) is a diagnostic method in which hydrogen ions within the body are excited by exposure to a magnetic field. The resulting signals are processed by a computer to create an image of the chest to define the location and extent of lung involvement.

Bronchoscopy is a visual examination of the windpipe and lung branches performed by a pulmonologist using a flexible scope. If the bronchoscopy is unrevealing, or ‘negative,’ a needle biopsy may be performed.

Needle biopsy, with CT-guidance, may be performed on suspicious areas in the lungs or pleura. Fine needle aspiration (FNA) uses a slim, hollow needle that is attached to a syringe. The needle is inserted into the suspicious mass and it is pushed back and forth to free some cells, which are aspirated into the syringe and are smeared on a glass slide for analysis. Large needle, or core biopsy, uses a large-bore needle to obtain a tissue sample for analysis.

Bone scan may also be performed to rule out suspicions of metastasis to the bones. Metastasis is the process wherein cancerous cells break away from the original tumor, travel, and grow within other body parts.

Blood tests may also be performed to look for lung cancer ‘markers’. For example, lung cancer may be indicated by abnormalities in the following.

  • Parathyroid hormone (PTH): Blood levels of PTH or PTH-related protein may help to distinguish lung cancer from cancer of the pleura or other diseases.
  • Carcinogenic antigen (CEA): This is a  cancer-specific immune system protein that is present in many adenocarcinomas, including lung adenocarcinoma. Increased preoperative levels of CEA usually suggest a poor prognosis. A CEA level greater than 50 may indicate advanced stage lung cancer and should discourage treatment by resection.
  • Cytokeratin fragment 19 (CYFRA21-1): A protein marker of lung cancer.

Management of lung cancer

Treatment options typically include one or more treatments, including surgery, chemotherapy, radiation therapy or targeted drug therapy. Table 1 enumerates the various treatment options available for the management of different types of lung cancer.

Treatment of lung cancer

Prevention of lung cancer

Lung cancer is associated with known risk factors. Many risk factors can be changed, but not all can be avoided.7

Tobacco

People who stop smoking and never start again have lower risk of developing lung cancer or of having lower lung cancer recurrence. Many products, such as nicotine gum, sprays, inhalers, patches and lozenges, as well as antidepressant drugs may be helpful to people trying to quit smoking. Never smoking lowers the risk of dying from lung cancer.

Environmental Causes

Cancer-causing agents that may be found indoors, especially in the workplace, include asbestos, radon, arsenic, chromium, nickel, tar and soot. These substances can cause lung cancer in people who have never smoked and combine with cigarette smoke to further increase lung cancer risk in smokers. Many countries are working to control these cancer-causing agents in the workplace. Air pollution may also increase the risk of lung cancer. Lung cancer rates are higher in cities with higher levels of air pollution.

Beta-Carotene

Heavy smokers who avoid taking beta-carotene supplements have higher risk of getting lung cancer compared with smokers who do take beta-carotene and may avoid further increasing their risk of lung cancer by consuming beta-carotene-rich food.

Diet and Physical Activity

A diet rich in fruits and possibly vegetables may help lower the risk of lung cancer, while heavy alcohol drinking may increase the risk of lung cancer. People who are physically active may have a lower risk of lung cancer than those who are not.

References

1. Rosen G. A history of public health. The Johns Hopkins University Press Baltimore, MD.

2. lberg AJ, Samet JM. Epidemiology of Lung Cancer. Chest. 2003; 123: 21S–49S.

3. American Cancer Society. Cancer Facts and Figures 2005.

4. International Agency for Research on Cancer (IARC). IARC Monographs on the Evaluation of Carcinogenic Risks to Humans and their Supplements: A complete list. Tobacco Smoking Monograph. 1986; volume 38.  

5. International Agency for Research on Cancer (IARC). IARC Monographs on the Evaluation of Carcinogenic Risks to Humans and their Supplements: A complete list. Tobacco Smoking and Tobacco Smoke. 2002; volume 83.  

6. U.S. Department of Health, Education and Welfare. Smoking and Health: Report of the Advisory Committee to the Surgeon General of the Public Health Service,1964.

7. Lung cancer prevention. National Cancer Institute. National Institutes of Health. 2006. Available at:http://www.cancer.gov/cancertopics/pdq/prevention/lung/Patient/page2