SUNDAY, Sept. 24 (HealthDay News) -- An abnormal mammogram can cause understandable worry. But what's the best next step a woman should take?

New research has found that a breast biopsy is the preferred follow-up procedure, even though several other test options exist and may be offered by physicians.

A recent report by the Agency for Healthcare Research and Quality (AHRQ) compared the effectiveness of biopsy, long considered the "gold standard," with four other tests. The other four tests were magnetic resonance imaging, or MRI; ultrasonography; positron emission tomography (PET) scanning; and scintimammography.

The report, titled Effectiveness of Noninvasive Diagnostic Tests for Breast Abnormalities, "focuses on a very specific question," said AHRQ Director Dr. Carolyn M. Clancy. "The question we were addressing was, are any of the other noninvasive tests sufficiently accurate to diagnosis cancer or to rule it out?"

A biopsy is accurate but invasive, requiring the taking of a sample of breast tissue and analyzing it for signs of cancer in a laboratory. So, researchers have been searching for noninvasive tests that would be as accurate.

The four tests assessed in the report, all suggested as substitutes for biopsies, weren't as accurate as a biopsy overall. They missed between 4 percent and 9 percent of breast malignancies in women at average risk, the report found, and probably would miss more cases than that among women at higher risk of the disease.

How accurate is accurate enough? "Some experts say a test would have to miss fewer than 2 percent to be considered sufficiently accurate," Clancy said.

It's hard to pinpoint the exact accuracy of biopsies, but a study published last year in the Annals of Surgery found that the "false-negative" rate for one type of biopsy, called a "core biopsy," was 6 percent, according to Fran Visco, the first president and spokeswoman for the National Breast Cancer Coalition in Washington, D.C.

In the AHRQ report, the researchers found that the use of MRI missed 38 cancers for every 1,000 women; ultrasound missed 50 tumors for every 1,000 women; and PET scans missed 76 per 1,000 women. Scintimammography, a nuclear medicine test method that uses a small amount of dye and a scanner to detect cancer, missed 93 tumors for every 1,000 women.

The report on the four noninvasive tests is valuable, Visco said. "My interest in the 2006 AHRQ report focuses on the fact that we move these technologies into clinical practice when we don't have the data that show they are effective. That adds to health-care costs and also doesn't serve women well."

Having access to solid data that proves a test is accurate will help women and the health-care system, she said.

Clancy added: "Findings in this study provide good information for women to have additional conversations with their doctors." If a doctor suggests one of the alternate tests after an abnormal mammogram, she said, "It would be reasonable to ask for a biopsy in lieu of these tests."

More information

To learn more about breast biopsies, visit the National Library of Medicine.