Image of x-ray of man's chest with lungs highlighted

What is lung cancer?

About lung cancer

Image of woman coughing in front of an office building

Our lungs enable us to breathe. When we inhale, air goes through our nose, down our windpipe (trachea), and into our lungs, where air spreads through tubes called bronchi. Oxygen from the air that we breathe in passes into the blood and is carried to the rest of the body.

Lung cancer is the uncontrolled growth of abnormal cells in the lungs, usually beginning in the cells lining the air passages. These abnormal cells do not act like normal lung cells and they do not develop into healthy lung tissue. Instead, they often form tumours and impair the functioning of the lung, affecting oxygen intake and regular bodily functions.

Primary lung cancer begins in the lungs, but cancer cells can also travel from another part of their body. This is known as secondary lung cancer.

How do lung cancers form?

Illustration of how lung cancer forms

Cells in the body contain DNA. When a cell divides into two cells, the new cell carries the exact DNA of the original. This is now the human body replenishes itself: old cells die and new ones are duplicated. In the case of cancer, an error or a mutation happens in a cell's DNA, and this abnormal cell divides itself, carrying over the mutation into the new cell. Such mutations may be caused naturally by aging, or through external factors such as cigarette smoke.

It has been found that a lung cancer cell is formed through a series of such mutations. Hence, lung cancer cells can be precancerous, that is, they have some form of mutation but still function normally as lung cells. As these cells multiply, the increase in the number of mutated lung cells start to impact the lung's function. If not treated early enough, these lung cancer cells may travel to other parts of the body and start growing there.

What are the causes and risk factors of lung cancer?

There are a number of known causes for lung cancer:

Smoking (primary and secondary)

Cigarette smoking is the most common cause of lung cancer. The risk of a smoker developing lung cancer is up to 20 times that of a non-smoker; more cigarettes and years smoked adds to this risk. It's not only cigarettes: smoking cigars, tobacco pipes and marijuana also put you at risk of lung cancer.

Secondhand smoke also increases one's risk of developing lung cancer by 30%. So, working in an environment where one is constantly exposed to smoke is a risk factor.

Personal and hereditary health

A small yet significant percentage of lung cancers may also be caused by a previous history of lung disease, previous smoke-related cancer, previous cancer treatment, lowered immunity (due to HIV/AIDS or drugs used to suppress immune system), metastasis of another cancer that has spread, or even a family history of lung cancer.

Indoor and outdoor air pollution

Outdoor pollution from burning fuels at industrial sites and diesel engine fumes on the roads, or particulates as well as indoor air pollution such as radon (a naturally occurring radioactive gas that comes from radioactive decay of uranium) which may enter homes through cracks in the wall or flooring, also pose a lung cancer risk.

Exposure to chemicals such as asbestos (breathing in the fibres), coal gas, silica, chromium, nickel and arsenic may increase the risk of lung cancer.

How can I prevent myself from getting lung cancer?

Don't smoke. If you are a smoker, seek help to stop smoking. If you are not a smoker, don't start.

Avoid secondhand smoke in smoking areas.

Keeping a good diet and exercise programme, plus getting sufficient sleep, will all help in general cancer prevention.

Avoid areas with heavy air pollution, such as industrial or haze-filled areas. Particulate matter (PM) comprises extremely small particles and liquid droplets in the air that can severely impact the heart and lungs when inhaled.