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Lung cancer

What is lung cancer?

Lung cancer is cancer that starts in the lungs. Cancer is a disease where cancer cells grow out of control, taking over normal cells and organs in the body.

Types of lung cancer

There are two major types of lung cancer. Each type of lung cancer grows and spreads in different ways. Each type may be treated differently.

Non-small cell lung cancer

This is the most common type of lung cancer. It usually spreads more slowly than other lung cancers. There are three major types of non-small cell lung cancer:

  • Squamous cell carcinoma
  • Adenocarcinoma
  • Large cell carcinoma
Small cell lung cancer
This is a less common type of lung cancer and it spreads faster than non-small-cell lung cancer. There are three major types of small cell lung cancer:

  • Small cell carcinoma
  • Mixed small cell/large cell
  • Combined small cell carcinoma

There are also other types of lung cancer.

Causes of lung cancer

Lung cancer is usually caused by smoking – but not always. Researchers say that more than 90% of lung cancers in men and at least 70% in women are directly caused by cigarette smoking1.

Lung cancer can also be caused by other things. Some people who have lung cancer have never smoked a day in their lives. Their cancer may be caused by something else, like:

  • Second-hand smoke. People who regularly breathe second-hand smoke have almost double the risk of getting lung cancer than people who stay away from smoke 1. It's a fact: Non-smokers who live or work in smoky air can get lung cancer from second-hand smoke.
  • Radon. Radon is a colourless, odourless gas found in the soil. Radon can enter buildings through cracks in the foundation or insulation, or through drains or walls. Radon can get trapped in basements and other places that don't have a lot of air flow (fresh air). People who have a high exposure to radon are at higher risk of lung cancer. Read more about radon, an invisible gas that can cause lung cancer.
  • Asbestos. Asbestos is a heat-resistant mineral found in some workplaces and homes. It has been used in brake pads, insulation, siding, and many other products. People who have a high exposure to asbestos are at higher risk of lung cancer. Read more about asbestos
  • Other toxic products: uranium, arsenic, some petroleum products may also increase the risk of developing lung cancer
Who is at risk of getting lung cancer?

People who are exposed to these things are most at risk of lung cancer:

  • Smoking cigarettes
  • Smoking cigars and pipes
  • Breathing in second-hand smoke
  • Being exposed to asbestos or radon
  • ...or a combination of any of the above risks

If you smoke and you are exposed to another risk factor (radon, asbestos, etc.) you are at much higher risk for lung cancer.

How can you lower your risk of getting lung cancer?
  • The best way to lower your risk of lung cancer is simple: Don't smoke. If you do smoke, quit. The sooner you quit smoking, the sooner your risk of lung cancer drops. It's never too late to quit smoking.
  • Stay away from second-hand smoke.
  • Check your home for radon, a odourless, invisible gas that can seep through walls and basements.
More about lung cancer


1. Percentage of lung cancer associated with smoking: "Probably more than 90% of lung cancers in men and at least 70% in women are directly attributable to cigarette smoking". Cancer Care Ontario, Cancer Incidence and Mortality in Ontario, 1964-2002.

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