Experts say that each year more than one million people worldwide die of lung cancer.It is the leading cause of cancer death in both men and women.

Last week, Dana Reeve died of lung cancer at the age of forty-four.The singer and actress became an activist for victims of spinal cord injuries after her husband's horse riding accident.She took care of "Superman" actor Christopher Reeve for nine years.He died in October of two thousand four.

Last August Dana Reeve announced that she had lung cancer.Smoking is linked to about ninety percent of cases.

But Dana Reeve did not smoke.

Researchers say this is true of up to thirty percent of American women who develop lung cancer.In fact, experts say a higher rate of non-smoking women get the disease than non-smoking men.

Studies have shown that men and women react differently to tobacco smoke.Scientists are not sure why.Some suggest that cells in women's lungs mighty be more easily damaged by smoking.There could be genetic or environmental reasons.

Experts say even people who do not smoke could still be considered "passive smokers" if they breathe other people's tobacco.Derek Raghavan is director of the Cancer Center at the Cleveland Clinic in Ohio.He thinks secondhand smoke causes at least half the cases of lung cancer in non-smokers.

The cause in Dana Reeve's case is not known.But Doctor Raghavan notes that singers and other people in the entertainment business often work around smokers.

A common sign of lung cancer is a cough that does not go away and gets worse over time.Other common signs include chest pain, coughing up blood, shortness of breath and repeated cases of pneumonia.

By the time most people feel sick enough to see a doctor, the cancer has spread too far to be treated effectively.The five-year survival rate is only about fifteen percent.

Treatment includes removing the growth.Chemotherapy drugs and radiation can help kill cancer cells and shrink the tumor.

There is no cure.And two support groups, the Lung Cancer Alliance and Women Against Lung Cancer, say there is not enough money for research.For now, researchers say the best way to fight lung cancer is to try to prevent it.

Dana Reeve leaves behind a thirteen-year-old son and Christopher Reeve's two adult children.

This VOA Special English Health Report was written by Cynthia Kirk.I'm Steve Ember.