Lung cancer overview

Illustration of lungsLung cancer is the #1 cancer killer in the United States today. Lung cancer kills more people than breast, cervical, colon, and prostate cancer combined, and does not generally show any symptoms until its late stages.

Where lung cancer starts

To understand lung cancer, we must first understand the lungs. The lungs are two sponge-like organs in the chest. The right lung has three sections, called lobes. The left lung has two lobes. It is smaller because the heart takes up more room on that side of the body. The lungs bring air in and out, taking in oxygen and getting rid of carbon dioxide gas, which is a waste product of the body.

The lining which surrounds the lungs is called the pleura. The pleura protects the lungs. The windpipe, or trachea, brings air down into the lungs, and divides into tubes called bronchi, which divide into smaller branches called bronchioles. At the end of these small branches are tiny air sacs known as alveoli.

Most lung cancers start in the lining of the bronchi. But lung cancer can also begin in other areas such as the trachea, bronchioles, or alveoli. Lung cancer usually takes many years to develop.

Causes of lung cancer

Undeniably, the most significant cause of lung cancer is cigarette smoke. Roughly 85% of lung cancers are diagnosed in former or current smokers; other cases may be caused by environmental exposure to materials like asbestos or uranium, genetics, or secondhand smoke.

Cigarette smoking

Packs Per Day


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Cigarette smoking causes 85% of all lung cancers--that's been roughly 180,000 cases per year, resulting in approximately 169.000 deaths. The more cigarettes a person has smoked, the higher their risk of lung cancer will be. The amount someone has smoked is often referred to as their pack years. To calculate pack years, multiply how many packs per day you smoked times how many years you smoked. However many years it would have taken you to smoke all the cigarettes you've smoke if you smoked them one pack a day is your pack years.

If you've quit smoking, your risk is lower than it would be if you had continued to smoke today but remains higher than if you had never smoked. If you want to minimize your risk of lung cancer, do not smoke. If you smoke, quit. If you don't smoke, don't start.

Other causes

Other causes

For the 10-15% of lung cancers that are diagnosed in nonsmokers, there are a number of potential causes:

  • Heavy exposure to asbestos, radon, uranium, arsenic, and other carcinogens

  • Genetic predisposition

  • Heavy exposure to secondhand smoke

  • Lung scarring from past illness

Additional risk factors

In addition to the direct causes listed above, there are a number of other risk factors to be aware of.

  • Family history. You are at an elevated risk of lung cancer if a blood-related parent or sibling has had lung cancer. In particular, your risk is elevated if this relative was diagnosed before the age of 50, which suggests that genetic factors played an important role.

  • Gender. Though more men are diagnosed with and die from lung cancer, recent research has indicated that women with the same smoking history and age as men are more likely to develop lung cancer. IELCAP released a study in July 2006 showing that with age and smoking history held constant, women were twice as likely as men to develop lung cancer. This was mitigated, however, by the finding that they were also less likely to die from the disease. Another recent study, released by researchers at Stanford University in February 2007, found that nonsmoking women were far more likely than nonsmoking men to develop lung cancer; they estimated that 20% of women diagnosed with lung cancer had never smoked. For more information, visit Women and Lung Cancer.

  • Race. It has been observed for some time that lung cancer diagnosis and mortality rates are higher among non-white patients. Higher rates of smoking have always been suspected as a key driver of this, as has the greater popularity of menthol cigarettes among African-American men. Recent research, however, suggests that some groups have other factors driving risk. A study released in January 2006 by University of Southern California (USC) Keck School of Medicine found that among smokers who smoked less than one pack per day, African-Americans and Native Hawaiians showed a much greater risk of developing lung cancer than other racial and ethnic groups. After controlling for a number of factors, the study was unable to identify why, exactly, these groups were more susceptible.

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