Higher levels of an enzyme that makes estrogen may be the hallmark of a more aggressive type of lung cancer in older women, a finding that could lead to earlier diagnosis and treatment, U.S. researchers said on Thursday.

They said measuring levels of the enzyme aromatase -- which naturally converts the hormone androgen into estrogen -- could be used to predict survival in women with early stage lung cancer who are over the age of 65.

And it may also suggest treatments that inhibit aromatase, which are already approved to treat breast and ovarian cancer, might be a possible new treatment for lung cancer.

"All indications suggest that this is a very powerful marker that lets us predict which patients have a higher likelihood of prolonged survival versus death from lung cancer," said Lee Goodglick, an associate professor in the Department of Pathology and Laboratory Medicine at UCLA, whose study was published in the journal Cancer Research.

The study also allows doctors to predict survival early in the disease process.

Goodglick and colleagues knew estrogen played a role in the development of lung cancer, just like it does in some breast cancers.

Studies in animals found a link between estrogen and aromatase in triggering the growth of lung cancer tumors. They studied tissue samples taken from 750 men and women.

What they found was a link between higher aromatase levels and aggressive lung cancer in women 65 and older. They did not find the higher enzyme levels in men or younger women.

The researchers are not sure why aromatase is a better predictor of lung cancer in women 65 and older, but it may have something to do with androgen, which declines steadily at that age.

They hope to study this in a larger group of people at many cancer centers across the country.

"We need to figure out all the strategies that a lung cancer cell uses to trigger and amplify the estrogen pathway," Goodglick said in a statement. "In women over 65, one trick the cancer cells appear to use is increasing aromatase."

Lung cancer is the second-most common cancer in women after breast cancer, according to the American Cancer Society. About 98,000 women will be diagnosed with lung cancer this year and more than 70,000 will die.