TUESDAY, May 13 (HealthDay News) -- While undoubtedly lifesaving for many women, mammography is far from perfect. But, undergoing breast ultrasound in addition to standard mammography can find more cancers in high-risk women, particularly those with dense breast tissue, a new study found.

But, the study authors noted, ultrasound also significantly increases the rate of false-positive readings.

"In our study participants, half of the breast cancers were found using mammography alone. By adding ultrasound, we found 78 percent of the cancers," said the study's lead author, Dr. Wendie Berg, a radiologist at an outpatient center in Lutherville, Md., affiliated with Johns Hopkins Medical Center.

However, identifying those extra cancers came with a cost of significantly more false-positive readings.

"With mammography, a woman has about a one in 40 chance that a biopsy will turn out not to be cancer. With the addition of ultrasound, it's one in 10," Berg said.

Results of the study, which was funded by the Avon Foundation and the U.S. National Cancer Institute, were published in the May 14 issue of the Journal of the American Medical Association.

Each year, more than 180,000 American women are diagnosed with breast cancer, and almost 41,000 will lose their lives to the disease. Death rates from breast cancer have been declining, possible due to earlier detection and diagnosis, according to the American Cancer Society.

The new study included almost 3,000 women recruited from 21 centers. The average age was 55 years old, and all of the women had a higher-than-normal risk of breast cancer.

The women were randomly assigned to receive either mammography alone or mammography plus ultrasound performed by a physician.

Forty women were diagnosed with breast cancer within a year of their initial screening. Mammography alone uncovered 20 cancers, 50 percent, while the combination screening technique found 31 of the cancers, or about 78 percent, according to the study.

That means for every woman screened, mammography alone will find 7.6 cancers, mammography plus ultrasound will detect 11.8 cancers, and three cancers will be missed altogether, the researchers said.

The study found that ultrasound was a good complementary screening tool for mammography, because it found cancers that mammography might miss.

"Ultrasound performs best in cases for which mammography performs weakest, i.e., in breast areas with dense fibroglandular tissue," Dr. Christiane Kuhl, with the Department of Radiology at the University of Bonn in Germany, wrote in an accompanying editorial in the journal. Kuhl also noted that the drawbacks to ultrasound include the frequency of false-positives, the cost of the test, and a lack of evidence that the test affects mortality.

Berg noted that there aren't currently enough physicians or ultrasound technicians trained for ultrasound to be a viable, widely used screening tool right now, even just for high-risk women.

"On average, physicians can only perform three to five ultrasounds per hour," said Berg, compared to as many as 50 mammograms in an hour, according to the editorial.

Dr. Julia Smith, director of the Lynne Cohen Breast Cancer Preventative Care Program at the New York University Cancer Institute and Bellevue Hospital in New York City, said, "I already do ultrasounds on women at risk. As a complementary test, ultrasound can be a very useful test. Also, we know it's relatively inexpensive and safe."

Magnetic resonance imaging (MRI) may be more effective than either mammography or ultrasound, and it's fast becoming a popular tool for breast cancer screening, but, Smith said, the cost of MRI is prohibitive.

Given limited health-care resources, Kuhl wrote that "mammography will probably remain the basis for breast cancer screening for the foreseeable future."

Smith said what's most important is for women to talk with their doctors about their individual risk of breast cancer, and then decide which screening tests would be most appropriate.

More information

To learn more about breast cancer screening options and current recommendations for screening, visit the American Cancer Society.

SOURCES: Wendie Berg, M.D., Ph.D., radiologist, outpatient center affiliated with Johns Hopkins Medical Center, Baltimore; Julia Smith, M.D., director, Lynne Cohen Breast Cancer Preventative Care Program, New York University Cancer Institute and Bellevue Hospital, New York City; May 14, 2008, Journal of the American Medical Association

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