A hair-loss drug that can also prevent prostate cancer may offer a third benefit by helping doctors detect the most aggressive prostate tumors earlier, U.S. and Israeli researchers reported on Tuesday.

They said they could dispel fears that finasteride might somehow cause the high-grade tumors.

Two studies published in the Journal of the National Cancer Institute show that the drug appears to be keeping the prostate gland small, making it easier to find dangerous tumors inside or on the surface.

"It appears that a man concerned about prostate-cancer risk, who is having a PSA test on a regular basis, will not only reduce his risk of prostate cancer if he takes finasteride, but will help find the cancers that pose the highest risk," Dr. Ian Thompson of the University of Texas Health Science Center at San Antonio said in a statement.

An estimated 219,000 U.S. men will this year be diagnosed with cancer of the prostate, a walnut-sized gland that makes fluid for semen, and 27,000 will die of it, according to the American Cancer Society.

Finasteride, available generically but also sold as a hair loss drug by Merck and Co under the brand name Propecia, can reduce the risk of prostate cancer by 25 percent.

Diagnosing prostate cancer is tricky. The gland can enlarge naturally, and it also produces a protein called prostate specific antigen or PSA.

Doctors can feel an enlarged gland with a finger, or can measure PSA in the blood. PSA goes up as the prostate enlarges, but it also rises if there is a tumor in the gland.

A biopsy can find cancer, but doctors take samples randomly and can easily get several pieces of healthy tissue instead of a nearby tumor.

When finasteride was studied for its potential in preventing cancer, researchers noticed that the men who did get cancer were slightly more likely to have aggressive tumors.

It was feared that finasteride itself somehow made cancer worse if it was already present, although it lowered the overall risk of cancer by nearly 25 percent.

Yael Cohen of Gamida Cell in Jerusalem and colleagues found that prostate size in the finasteride group was 25 percent smaller than in men who got placebos -- making it easier to find the tumors.

Dr. Scott Lucia of the University of Colorado Health Sciences Center in Denver and colleagues made similar findings.

"This report ... should help lessen fears that finasteride somehow causes more aggressive prostate cancer," Dr. Frank Meyskens at the University of Texas Southwestern, who helped coordinate the original trials, said in a statement.