Dana Reeve, widow of Superman actor Christopher Reeve, has been diagnosed with lung cancer. Warned that a tabloid would break the news, she went public on the Christopher Reeve Paralysis Foundation Web site: "I have an excellent team of physicians and we are optimistic about my prognosis," she said.

Lung cancer is the leading cause of death in the United States and a major killer throughout the world. Nearly 90% of the cases are linked to smoking. More than 10% of the victims are -- like Dana Reeve -- non-smokers. And for reasons not yet well understood, women in that group are twice as likely as men to get the disease.

Derek Raghavan is director of the Cleveland Clinic and a cancer researcher. He says second-hand smoke is a major threat. "Many of the people who list themselves correctly as never having smoked a cigarette have actually inhaled a lot of passive smoke," he says. "You'll find that people who are in the entertainment business, if they work in clubs, particularly in the days when there was smoking allowed, have been inhaling smoke for years. I think in truth at least half the cases of lung cancer in non-smokers are the sad situation where their parents smoked or their loved ones smoked or they worked in a smoky environment."

Mr. Raghavan says researchers are also looking at factors other than second-hand smoke that may cause lung cancer in non-smokers. "There is a lot of rubbish in the air we breathe," he says. "For example, there is a gas called radon that sometimes accumulates in basements and when people go down to the basement in the winter, that is a risk factor."

The researcher notes that women in China who cook with a wok have a higher chance of getting lung cancer because some of the oils they use are cause cancer.

Asbestos, a fibrous industrial material whose use is now limited or banned in many countries, including the United States, is also linked to the disease.

Lung cancer symptoms -- shortness of breath, chest pain and coughing up blood -- occur in only about one quarter of the cases. The cancer claims its victims quickly. Only 15% of those diagnosed with the disease survive as long as five years.

"Frankly what I think what we need to do as a community is to stop smoking. And, we need institutions (to do the same)," says Derek Raghavan. "I work at the Cleveland Clinic, and we have 33,000 employees at 12 sites. We went smoke-free on July 4th. And, we have dozens of former smokers who have been able to quit with our help. I think that is the way to do it. Businesses, schools and institutions need to encourage their employees just not to do it in the first place."

Dana Reeve -- an activist for paralysis research with husband Christopher in the years after the actor's horseback riding accident -- says that as she faces her battle with lung cancer, she finds strength in the courage he showed. In an interview following his death in 2004, she said Christopher Reeve's spirit has never left her.

"It is kind of mystical, but one person said he will always be with you," she told NBC's Katie Couric. "I think that a person cannot love you that much without the energy staying. And that is kind of a comfort and feels like it is true."

In a statement on her Web site, Dana Reeve says of her late husband: "I look to him as the ultimate example of defying the odds with strength, courage, and hope in the face of life's adversities. And like the 80,000 other American women, and 90,000 American men who will be diagnosed with lung cancer this year, Dana Reeve will need all the strength, courage and hope she can muster to defy the odds, and live.