Causes of Lung Cancer in Non-Smokers

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Causes of Lung Cancer in Non-Smokers. istockphoto.com

When we think about lung cancer, we often think of the most common cause in people who smoke: cigarettes.  But lung cancer occurs in people who have never smoked as well.  In fact, lung cancer in never-smokers is considered the 6th or 7th most common cause of cancer deaths in the United States.

What causes lung cancer in people who haven't smoked, and why is it so important to further research into the causes?

 In addition, how does the stigma of lung cancer - that is the general public'a perception that people "deserve" lung cancer because they smoked - affect non-smokers?

Defining Non-Smokers

It's important to begin by defining what we mean by non-smokers (in this case never smokers.)  After all, many teenagers take a puff or two but never become active smokers.  A never-smoker is defined as someone who has smoked fewer than 100 cigarettes during their lifetime.

Why is it Important to Look at Causes?

With most cases of lung cancer caused by smoking, research has often focused on how tobacco causes lung cancer, and on ways to help people quit smoking.  Though necessary, in some ways this is unfortunate because research into the possible causes in non-smokers has taken a back seat.  It's not only the general public that lacks awareness about lung cancer in non-smokers, but this includes many health care providers as well.

 A quick look at some statistics may drive this point home.  

Statistics Regarding Lung Cancer in Non-Smokers (Never Smokers)

  • Roughly 10 to 15 percent of lung cancers occur in never smokers.  Around 20 percent of women who develop lung cancer have never smoked.
  • In 2014, it's expected that  40,000 women will die from breast cancer (this includes smokers, former smokers, and never-smokers.)  It's expected that 72,330 women will die from lung cancer.  Doing a few simple calculations, this would mean that 14,466 never-smoking women are expected to die from lung cancer. 
  • Unlike the recent drop in lung cancer deaths among men, lung cancer in young non-smoking women appears to be increasing.

More about lung cancer in non-smokers:

Known Causes of Lung Cancer in Non-Smokers

  • Radon - Exposure to radon in the home is the leading cause of lung cancer in people who have never smoked.  It's estimated that 21,000 people die each year in the United States due to radon-induced lung cancer.
  • Occupational Exposures On-the-job exposures to chemicals and substances may account for 13 to 29% percent of lung cancers.  This article discusses how to know if you may be exposed to cancer-causing substances at work, and what to do about it if you are.
  • Secondhand Smoke - Exposure to secondhand smoke (known as passive smoking) is responsible for around 3,000 lung cancer deaths yearly.
  • Asbestos - Exposure to asbestos - either at work or doing a home remodeling project - raises the risk of developing both lung cancer and mesothelioma.
  • Genetics/Heredity - Heredity plays a greater role in lung cancer among non-smokers than among smokers.  This article discusses risk seen in families.  Recently it's been found that mutations in the "breast cancer gene" BRCA2, raises the risk of developing lung cancer.  A rare genetic mutation – an T790M EGFR mutation (note: there are many types of EGFR mutations) results in a 31 percent lifetime risk of nonsmokers developing lung cancer.  This rare mutation is inherited in an autosomal dominant fashion – meaning that if a parent carries the gene, 50 percent of their children will inherit the gene.  Several other gene mutations have been associated with lung cancer in non-smokers, especially in Asian populations.
  • Air Pollution
  • Indoor Coal Smoke for Heating and Cooking  
  • Exposure to Diesel Exhaust Fumes

Unknown and Possible Causes of Lung Cancer in Non-Smokers

  • Granite Countertops - Since radon gas may be released from granite, there has been some concern recently about the potential for granite countertops to contribute to lung cancer risk.  If you have any concerns, this article discussing what we currently know will let you know how to test for radon due to granite countertops in your home.d
  • Human Papillomavirus (HPV) - Recent studies have found the presence of HPV in lung tumors.  It's not known at this time, though, if this association has anything to do with causation.  It is thought that HPV may contribute to EGFR mutations seen in lung cancer - at least in Taiwan. 

Next Steps:

Since we don't currently have a lung cancer screening test for non-smokers, it's important to be aware of possible symptoms if you've never smoked.  Due to the types of lung cancers seen in non-smokers, the symptoms of lung cancer in non-smokers are often different, and more subtle, than those in smokers.

Understanding that lung cancer does occur in non-smokers can help you educate your family and friends.  Here are a few articles which discuss important differences in greater detail:

Sources:

American Cancer Society. Why Lung Cancer Strikes NonSmokers. Updated 1028/13. http://www.cancer.org/cancer/news/why-lung-cancer-strikes-nonsmokers

Hosgood, H. et al. Household coal use and lung cancer: systematic review and meta-analysis of case-control studies, with an emphasis on geographic variation. International Journal of Epidemiology. 2011. 40(3):719-28.

Li, C. et al. Genetic variations in TERT-CLPTM1L genes and risk of lung cancer in Chinese women nonsmokers. PLoS One. 2013. 8(5):e64988.

Markowitz, S. et al. Asbestos, asbestosis, smoking, and lung cancer. New findings from the North American insulator cohort. American Journal of Respiratory and Critical Care Medicine. 2013. 188(1):90-6.

Tung, M. et al. Association of epidermal growth factor receptor mutations with human papillomavirus 16/18 E6 oncoprotein expression in non-small cell lung cancer. Cancer. 2013. 119(18):3367-76.

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