Dana Reeve - widow of Superman actor Christopher Reeve and advocate for victims of spinal cord injuries - died late Monday of lung cancer at the age of 44. Dana Reeve is among a growing group of non-smoking women who contract and die from the disease.

Dana Reeve had a nagging cough for about a year. It started in 2004, a few months after her husband's death. In an interview after she got the diagnosis she expressed surprise considering the risk factors for the disease. "I don't live in the city," she said on ABC television. "I don't work in a high-risk environment, and I am not a smoker. So it was never anything that would occur to me that I would get lung cancer, but the more I have learned about lung cancer is that it is becoming much more random, and it is striking women who are under 50 and are non-smokers and not in a risk environment."

Lung cancer is the leading cause of cancer deaths in the United States and a major killer throughout the world. Nearly 90 percent of the cases are linked to smoking. The other 10-plus percent of the victims are - like Dana Reeve - non-smokers. And for reasons not yet well understood, a greater proportion of women who develop lung cancer are non-smokers compared to men who get the disease.

Derek Raghavan is the director of the Cleveland Clinic Taussig Cancer Center.  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." These are people, he says, "in the entertainment business," adding, "If they worked in clubs, particularly in the days when there was smoking allowed, they 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."

Raghavan says researchers are looking at other factors too. "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," he says. "There is a lot of rubbish in the air that we breathe in. And, then there are unexpected and funny things. In China some of the women who cook their evening meal using a wok use some oils that are cancer-causing, and they have a higher chance of getting lung 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 fifteen percent of those diagnosed with the disease survive as long as five years.

Some researchers recommend people at high risk have a special CT scan. However, other experts are awaiting the results of a large-scale clinical trial of such imaging tests which is currently underway.

Until early diagnosis is possible, American Cancer Society official Len Lichtenfeld advises people not to start smoking, and if you do to stop. "If there is some good that comes out of the situation with Ms. Reeve," he says, "it is a reminder that this is a disease that for many people can be prevented and unfortunately as in Ms. Reeve's case it is a situation where that was not the case."

174,000 new cases of lung cancer are predicted in the United States this year. One bit of good news: The death rate among men is declining, a development Dr. Lichtenfeld says is linked to the decreased use of tobacco products.