By Julie Steenhuysen

CHICAGO (Reuters) - A screening schedule that alternates between a breast MRI and a mammogram every six months may do a better job of spotting early cancers in high-risk women than an annual exam, U.S. researchers said on Saturday.

Women who are at high risk for breast cancer currently get a yearly mammogram and a more-sensitive magnetic resonance imaging or MRI test. The screening tests are typically done at the same exam.

Researchers at the University of Texas M.D. Anderson Cancer Center wondered if alternating the tests every six months would allow them to catch cancers earlier, when they have a better shot at a cure.

"We wanted to detect cancers early in this population since they are at high risk," Dr. Huong Le-Petross, who presented her findings at a breast cancer meeting in San Antonio, Texas, said in a telephone interview. "Earlier detection means smaller lesions."

Le-Petross and colleagues reviewed the charts of 334 women at high risk of developing breast cancer.

The women were considered high risk if they had a family history of breast and ovarian cancer, a personal history of breast cancer, a biopsy indicating precancerous changes or a 20 percent or higher lifetime risk of developing breast cancer.

Of the 334 women, 86 underwent the screening rotation and had undergone at least one MRI screening.

All participants were given a clinical breast exam every six months and were followed for about two years.

Of those in the screening rotation, the doctors found nine cancers. Five showed up only on MRI, three were found by both mammography and MRI, and one very early cancer was overlooked by both techniques but found on a later exam.

"We found that MRI picked up the majority of cancers, while mammography picked only three out of the nine," Le-Petross said.

Le-Petross said the findings suggest the alternating rotation may increase the chances of picking up cancers earlier. She said many of the cancers caught by the MRIs were not seen on the mammogram six months earlier.

She said the study also highlights the greater sensitivity of MRI screening for high-risk women with breast cancer.

Some studies have shown a breast MRI can detect breast cancers very early in high-risk women, but they cost $1,000 to $1,500 per test and they have a high rate of false positives.

Le-Petross said the study was ongoing and it is too early to say if this screening program will save lives.

According to the American Cancer Society, about 1.3 million women are diagnosed with breast cancer a year and an estimated 465,000 are killed by it.

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