What Is the Most Common Type of Lung Cancer in Non-Smokers?

Types of Lung Cancer in Non-Smokers vs People Who Smoke

man holding up a hand saying no to a pack of cigarettes
What type of lung cancer is most common in non-smokers?. Istockphoto.com/Stock Photo©BrianAJackson

 I’ve often been asked what type of lung cancer is most common in non-smokers. There are a few parts to this answer, but first, since you asked this question, it’s important to say that understanding that lung cancer occurs in non-smokers means you’re a step ahead of the crowd.

Lung cancer not only occurs in people who have never smoked, but lung cancer in never smokers is the 6th leading cause of cancer deaths in the United States.

When discussing this question it can help to distinguish statistics and studies which speak of non-smokers vs those that refer to never smokers. The category of non-smokers includes both never smokers and people who smoked at one time but have now quit (former smokers.) The term never smokers refers to people who have smoked 100 cigarettes or less during their lifetime.

At the current time, roughly 10 to 15 percent of people who develop lung cancer are never smokers,  roughly 39 percent are active smokers, and 49 to 54 percent are former smokers. Added together, the majority of people are non-smokers at the time of a lung cancer diagnosis.

To answer this question it helps to break lung cancer down step by step into the different types.

Non-Small Cell Lung Cancer vs Small Cell Lung Cancer

There are 2 major types of lung cancer, non-small cell lung cancer and small cell lung cancer. These types are named according to the appearance of the cancer cells under the microscope, with small cell cancers being composed of, not surprisingly, small, abnormal appearing lung cells.

Non-small cell lung cancer accounts for 85 to 90 percent of lung cancers and is the most common major type of lung cancer found in non-smokers. It is also, due to numbers, the most common major type of lung cancer found in people who smoke. Small cell lung cancer accounts for 10 to 15 percent of lung cancer and is much more strongly associated with smoking.

It's thought that only around 1 percent of people who develop this type of lung cancer have never smoked.

Types of Non-Small Cell Lung Cancers and Smoking Status

Non-small cell lung cancer is further broken down into 3 different types:

Lung adenocarcinoma is the most common type of non-small cell lung cancer and is the most common type of lung cancer found overall in both non-smokers and smokers. It is also by far the most common type of lung cancer in women and young adults with lung cancer.

Lung adenocarcinoma accounts for 30 percent of lung cancers in male smokers, and 40 percent of female smokers. In contrast, this type of tumor accounts for 60 percent of lung cancers in non-smoking men, and 80 percent of lung cancers in non-smoking women.

The other forms of non-small cell lung cancer include squamous cell carcinoma of the lungs which accounts for 25 to 30 percent of non-small cell lung cancers and large cell lung cancer which is present in 10 to 15 percent of non-small cell lung cancers.

 These cancers are both much more common in people who have smoked. Not all cancers are strictly defined by one of these subtypes, and it's possible for a lung tumor to have regions of lung adenocarcinoma as well as squamous cell carcinoma, as well as other combinations of tumor characteristics.

Why Would Smokers and Non-Smokers Develop Different Types of Lung Cancer?

One possible difference in the types of lung cancer seen in smokers and non-smokers may be related to the particular areas of the lung most affected by the lung cancer carcinogens in question, whether this is tobacco smoke, radon gas, occupational chemicals, or other exposures. It may also be related to the type of damage (DNA mutations) caused by the particular carcinogens. At this time this question remains mostly unanswered. It's interesting to point out that with the addition of filters to cigarettes, the most common types and locations of lung cancers changed. Years ago cancers such as squamous cell non-small cell lung cancer and small cell lung cancer were more common. These cancers tend to begin in the larger airways entering the lungs (the bronchi.) After filters were adopted, lung adenocarcinoma became much more common. These cancers tend to arise in and near the smaller airways in the periphery of the lungs.

Why is This Information Important?

Lung cancer in non-smokers is a different disease in many ways. In addition to the types of lung cancer, there are also differences between non-smokers and smokers with regard to which treatments are most effective, and even survival rates.

Sources:

College of American Pathologists. Lung Adenocarcinoma. Accessed 08/28/15. http://www.cap.org/apps/docs/reference/myBiopsy/LungAdenocarcinoma.pdf

Subramanian, J., and R. Govindan. Lung cancer in never smokers: a review. Journal of Clinical Oncology. 2007. 25(5):561-70.

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