CHICAGO: Using ultrasound in addition to mammography helped doctors spot significantly more breast cancers in high-risk women compared with mammograms alone, but it also resulted in four times as many false alarms, researchers said Tuesday.

“Mammograms saw only half of the breast cancers that were present,” said Dr. Wendie Berg of American Radiology Services at Johns Hopkins at Green Spring Station in Lutherville, Md., who did the study. “If we added ultrasound to mammography, we saw 78 percent of the cancers.”

Dr. Berg, whose study appears in the Journal of the American Medical Association, said most of the cancers found with ultrasound were small invasive cancers that had not spread to the lymph nodes. “These are types of cancers that we most need to be finding,” she said.

The study was designed to see whether ultrasound might improve the chances of finding breast cancer in high-risk women with dense breast tissue, which makes cancer harder to see on a standard mammogram, a type of X-ray. Dr. Berg and her colleagues standardized the scanning technique and interpretation criteria for the ultrasound examination. They studied 2,809 women 25 or older from April 2004 to February 2006 at 21 sites, who underwent either a mammogram alone or a mammogram and ultrasound.

Within the first year of screening, breast cancer was diagnosed in 40 women. Mammography alone found 12 cancers, and mammography with ultrasound found 20. The initial screening missed seven cancers that were found by later tests, and one cancer detected when a lump was felt.

Adding ultrasound increased the rate of false positives fourfold. About 1 in 40 women who had a mammogram alone had an unnecessary biopsy, Dr. Berg said. In the group that got both a mammogram and an ultrasound, false positives rose to 1 in 10 women.

“That causes a lot of unnecessary stress and, of course, adds costs to the medical system,” Dr. Berg said.

She and her colleagues planned an analysis to determine whether it would make sense to add ultrasound as a routine test for high-risk women.