CHICAGO (AFP) -- A hormone that regulates blood pressure has been shown to reduce lung cancer tumors in mice and may provide a new way to treat this type of malignancy, a new study said.

In experiments on laboratory mice that had been injected with human lung cancer cells, researchers found that the ones treated with the hormone, angiotensin-(1-7), saw their tumors shrink by 30 percent, according to scientists at Wake Forest University School of Medicine.

In contrast, in mice treated with saline, the tumors more than doubled in size over the 28 days of the experiment.

The researchers were alerted to the potential anti-cancer properties of the hormone by earlier studies which found that rates of lung cancer were lower in people being treated for high blood pressure with a class of drugs known as ACE inhibitors.

These drugs increase levels of angiotensin-(1-7) in the bloodstream. The hormone helps to lower blood pressure by dilating, or enlarging, blood vessels.

The researchers believe the hormone's anti-cancer effect is due to its reduction of levels of an enzyme called COX-2 or cyclooxgenase-2, which stimulates cell growth.

"It acts like a dimmer switch on a light," said Patricia Gallagher, one of the authors of the paper, and a researcher at Wake Forest University Baptist Medical Center in Winston Salem, North Carolina.

COX-2 is found at higher levels in 70 to 90 percent of malignant lung tumors.

Researchers in the university's Comprehensive Cancer Center plan to start a small trial of the hormone in human lung cancer patients next month.

"We hope that our clinical trials of angiotensin-(1-7) will lead to the identification of an effective new cancer treatment," said Frank Torti, director of the center.

Lung cancer is the most deadly of all cancers. About 14 percent of people with the malignancy survive past the five-year mark, according to background information in the study, which appears in the journal Cancer Research.