What is Lung Cancer?
Lung Cancer

Lung Cancer is cancer that forms in tissues of the lung, usually in the cells lining air passages. These abnormal cells do not carry out the functions of normal lung cells and do not develop into healthy lung tissue. As they grow, the abnormal cells can form tumors and interfere with the functioning of the lung.

Types of lung cancer

There are two main types of lung cancer. These two types of cancers grow, spread, and are treated in different ways.

The two main types are small cell lung cancer and non-small cell lung cancer. These types are diagnosed based on how the cells look under a microscope.

  • Non-small cell lung cancer (NSCLC) is the most common type of lung cancer accounting for about 80% of all cases. Most people diagnosed with lung cancer have non-small cell lung cancer. It doesn’t grow and spread as fast as small cell lung cancer, and is treated differently.
  • The three main types are Adenocarcinoma, Squamous cell carcinoma and Large cell carcinoma.
  • Small cell lung cancer (SCLC) makes up about 20% of all lung cancer cases. This type is the most aggressive and rapidly growing of all the types. SCLC is strongly related to cigarette smoking with only 1% of these tumors occurring in non-smokers. SCLC metastasizes rapidly to many sites within the body and is most often discovered after metastasis. There are three types of small cell lung cancer named for the kinds of cells found in the cancer and how the cells look under a microscope.
  • Small cell carcinoma (oat cell cancer).
  • Mixed small cell/large cell carcinoma.
  • Combined small cell carcinoma.



Lung cancer has been the most common cancer in the world for several decades, and by 2008, there were an estimated 1.61 million new cases, representing 12.7% of all new cancers. It was also the most common cause of death from cancer, with 1.38 million deaths (18.2% of the total).
The majority of the cases now occur in the developing countries (55%). Lung cancer is still the most common cancer in men worldwide (1.1 million cases, 16.5% of the total).

Symptoms of lung cancer

The signs and symptoms of lung cancer can take years to develop and may not appear until the disease is advanced.

Symptoms of lung cancer in the chest:

  • Coughing, especially if it persists or becomes intense
  • Pain in the chest, shoulder, or back unrelated to pain from coughing
  • A change in color or volume of sputum
  • Shortness of breath
  • Changes in the voice or being hoarse
  • Harsh sounds with each breath (stridor)
  • Recurrent lung problems, such as bronchitis or pneumonia
  • Coughing up phlegm or mucus, especially if it is tinged with blood
  • Coughing up blood

If the original lung cancer has spread, a person may feel symptoms in other places in the body. Common places for lung cancer to spread include other parts of the lungs, lymph nodes, bones, brain, liver, and other organs in the body.

Risk factors for lung cancer

Smoking: Smoking causes nearly 9 out of 10 cases (86%). A further 3% of cases of lung cancer are caused by exposure to second hand smoke in nonsmokers (passive smoking) and about 90% of lung cancers arising as a result of tobacco use. Pipe and cigar smoking can also cause lung cancer. Tobacco smoke contains over 4,000 chemical compounds, many of which have been shown to be carcinogenic. The two primary carcinogens in tobacco smoke are chemicals known as nitrosamines and polycyclic aromatic hydrocarbons.

  • The more you smoke, the more likely you are to get lung cancer but it is the length of time you have been a smoker that is most important.
  • Starting smoking at a young age greatly increases the risk
  • As soon as you stop smoking your risk of lung cancer starts to go down
  • Passive smoking (breathing in other people's cigarette smoke) can increase the risk of lung cancer.

Passive smoking: Passive smoking, or the inhalation of tobacco smoke from other smokers, is also an established risk factor for the development of lung cancer. Research has shown that non-smokers who reside with a smoker have a 24% increase in risk for developing lung cancer when compared with other non-smokers.

Exposure to radon gas: Radon is the second biggest cause of lung cancer after smoking. Radon gas is a naturally occurring radioactive gas which comes from tiny amounts of uranium present in all rocks and soils. The radon gas can build up in homes and other buildings.

Exposure to chemicals: A number of substances that occur in the workplace may cause lung cancer. In particular, these include asbestos, silica, and diesel exhaust.

Air pollution: Based on a large European study, researchers think that 5-7% of lung cancers in non-smokers are due to outdoor air pollution. The use of coal for cooking and for heating the home, and a high level of smokiness in the home, has been shown to increase lung cancer risk.

Previous lung disease: Having had a disease that caused scarring in the lungs may be a risk factor for a type of lung cancer called adenocarcinoma of the lung.

Family history of lung cancer: If you have a first degree relative with lung cancer your risk of lung cancer is increased by 51%. The risk is even greater if a brother or sister has lung cancer. This risk is regardless of whether or not you smoke.

Lowered immunity: HIV and AIDS lower immunity and so do drugs that people take after organ transplants. An overview of research studies shows that people with HIV or AIDS have a risk of lung cancer that is 3 times higher than people who do not have HIV or AIDS. People who take drugs to suppress their immunity after an organ transplant have double the usual risk of lung cancer.

The presence of certain diseases of the lung, notably chronic obstructive pulmonary disease (COPD), is associated with a slightly increased risk (four to six times the risk of a nonsmoker) for the development of lung cancer even after the effects of concomitant cigarette smoking are excluded.

Personal history of lung cancer
Survivors of lung cancer have a greater risk than the general population of developing a second lung cancer. In survivors of small cell lung cancers (SCLCs) the risk for development of second cancers approaches 6% per year.

Workplace exposure: Studies have shown a link between being exposed to the following substances and an increased risk of lung cancer:

  • Asbestos.
  • Arsenic.
  • Chromium.
  • Nickel.
  • Radon gas.
  • Tar and soot.

These substances can cause lung cancer in people who are exposed to them in the workplace and have never smoked. The risk of lung cancer is higher in people who are exposed and also smoke.
Beta carotene supplements in heavy smokers: taking beta carotene supplements (pills) increases the risk of lung cancer, especially in smokers who smoke one or more packs a day. The risk is higher in smokers who have at least one alcoholic drink every day.