Even though smoking is the leading cause of lung cancer, 10 to 15 percent of lung cancer patients are non-smokers. So what is the cause in those cases?

This year alone, an estimated 25,000 Americans who never picked up a cigarette are going to be diagnosed with lung cancer. And the majority of those patients will be women.

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VIDEO: Dr. Robert Keenan

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Dr. Robert Keenan of Allegheny General Hospital said, ”For women, lung cancer is on the increase. They seem to make up the greater proportion of people who never smoked.”

Keenan also said genetics, along with environmental factors, may play a big role in non-smokers' lung cancers. “It may be hormonal or related to the fact on size, women's lungs are a bit smaller than men's. It may be that the environmental issues, second-hand smoke concentrates the toxics in a woman's lung compared to men's lungs,” said Keenan.

Keenan said there is now research that indicates second-hand smoke may be more dangerous than first-hand smoking.

The American Cancer Society said exposure to radon gas, which is found in many homes in Pennsylvania, can be a risk factor for lung cancer. Also, exposure to asbestos is a possible cause of lung cancer.

While many women worry about breast cancer, it may be time to be concerned about lung cancer.

Keenan said, ”Over the last year or two lung cancer has surpassed breast cancer and any other cancer as the leading cause of death for women.”

Click here for more information about Dana Reeve and lung cancer.