Cigarette smoking causes almost 90 percent of all lung cancers. So, it's not surprising that two of my close friends with lung cancer protested, "But I never smoked!"
In the U.S., however, about nine percent of the lung cancers in men and 19 percent in women occur in people who have never smoked -- defined as less than 100 cigarettes over a lifetime.
Other causes of lung cancer
The two most common causes of lung cancer in never-smokers are exposure to second hand smoke and exposure to radon. While second hand smoke is usually avoidable, radon is a natural radioactive gas that you can't see, smell or taste. Radon can seep into houses (usually in the basement) from naturally occurring uranium in the soil. (See: Radon and Lung Cancer.)
Lung cancer in never-smokers differs in at least two major respects from lung cancer in smokers:
* When examined under a microscope, certain types of cancer cells are more commonly found in cancerous tissues of never-smokers than in lung cancers present in smokers.
* Never-smokers more often have mutations in the gene for epidermal growth factor receptor (EGFR). These mutations foster the harmful, uncontrolled growth of cells that is characteristic of cancer.
These differences in microscopic appearance often make it possible to treat lung cancer in never-smokers with drugs that overcome the ill effects of the mutations in EGFR.
Diagnosis often comes late
Lung cancer in both smokers and never-smokers is usually first detected in advanced stages of the disease because the most common symptoms -- cough, chest pain, and shortness of breath -- are not particularly specific. Diagnosis can be delayed even further in never-smokers because doctors may not consider the possibility that they might have lung cancer.
Unfortunately, survival rates appear equally dismal in smokers and in never-smokers. However, some never-smokers do appear to have one therapeutic advantage. Those with mutations in EGFR (as described above) may respond to two drugs, gefitinib (Iressa) and erlotinib (Tarceva). While erlotinib appears more effective, both may be used after unsuccessful chemotherapy, or as primary therapy instead of chemotherapy in some cases.
Preventing lung cancer
Of course, the best way to prevent lung cancer is not to smoke. Also, never-smokers may reduce their chances of lung cancer by avoiding smoke-filled rooms. Finally, check your home for radon, which may be seeping in through fixable cracks in basements or walls. Visit the U.S. Environmental Protection Agency website for more information about radon.
By Simeon Margolis, M.D., Ph.D.
