In men who get lung cancers, only about 6 to 8 percent have never smoked. When nonsmoking men get lung cancer, it can be from inhaling second-hand smoke, having a genetic predisposition to the disease, or through occupational or environmental exposure. A generation ago, asbestos was the key exposure culprit in lung cancer among nonsmoking men. Since asbestos is no longer widely used, the biggest exposure danger is radon, a known carcinogen or cancer-causing agent. Radon gas comes from the radioactive breakdown of naturally occurring uranium and other elements in soil and rocks that is released into the air we breathe and the homes in which we live. Shale adds to radon levels in different parts of the country, including western Pennsylvania, where there are large deposits of Marcellus shale underground. Of all the women who get lung cancer, nonsmoking women make up about 18 to 20 percent of cases. Second-hand smoke is a prime cause of these cancers, particularly in the Black community where fewer women smoke cigarettes but many are exposed to second-hand smoke from male smokers in the household. Hormones also play a part in lung cancer in women. Researchers at the University of Pittsburgh were among the first to link female hormone estrogen to genetic mutations in lung tumors in women. Estrogen receptors ERα and ERβ have been detected on lung cancer cells and recent evidence suggests that hormone replacement therapy may increase both the incidence of, and mortality from, lung cancer in women. David O. Wilson, MD, MPH, is associate director of the Lung Cancer Center at UPMC Hillman Cancer Center Editor's Note: This article was originally published on January 30, 2018, and was last reviewed on July 13, 2023.