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Noninvasive Tests May Miss Breast Cancer, AHRQ Study Finds

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Press Release Date: February 9, 2006

Four common noninvasive tests for breast cancer are not accurate enough to routinely replace biopsies for women who receive abnormal findings from a mammogram or physical examination, according to a study released today by HHS' Agency for Healthcare Research and Quality (AHRQ).

Today's report is the second from AHRQ's new Effective Health Care Program, which compares the effectiveness of different treatments for health conditions. The report finds that each of the four tests—magnetic resonance imaging, ultrasonography, positron emission tomography scanning, and scintimammography—would miss a significant number of cases of cancer, compared with immediate biopsy for women at high-enough risk to warrant evaluation for breast cancer.

Mammography and physical examination are both used to detect the possibility of breast cancer. A woman receiving an abnormal mammogram or physical examination needs further confirmation to determine whether cancer is present. Currently, confirmation is recommended through a tissue biopsy, either by surgical excision or needle sampling.

Only about one in five women currently getting a biopsy for an abnormal mammogram or breast examination has breast cancer. The need for confirmation of the mammogram means some 80 percent of women with an abnormal mammogram must undergo the biopsy procedure, even though they ultimately prove not to have cancer. Accurate noninvasive tests could reduce the number of women needing to undergo a biopsy.

However, AHRQ's Comparative Effectiveness Review, Effectiveness of Noninvasive Diagnostic Tests for Breast Abnormalities, indicates that four common tests would miss about 4 percent to 9 percent of cancer cases among women testing negative who have average risk for the disease, with potentially more missed cancers among women at higher risk.

"So many women today undergo biopsies only to learn they do not have breast cancer. Hopefully, noninvasive tests can continue to improve so that in the future, there will be a viable alternative to biopsy," said AHRQ Director Carolyn M. Clancy, M.D. "But early and accurate diagnosis of breast cancer is crucial, and at this time, biopsies remain the most effective technique when mammography or physical examination reveals a potential problem."

The four tests reviewed in the study, and their results, were:

  • Magnetic resonance imaging (MRI)—MRI images are created by recording signals generated after radio frequency excitation of nuclear particles exposed to a strong magnetic field. Typically for breast imaging, dedicated breast coils (used to generate the magnetic field) are used—a woman lies prone with her breasts in close proximity to the coils. A contrast agent is given intravenously to highlight concentrations of blood vessels (e.g., around a tumor). For every 1,000 women who had a negative MRI, about 962 would have avoided an unnecessary biopsy, but 38 would have missed cancers.
  • Ultrasonography—Ultrasound uses high-frequency sound waves that reflect at boundaries with different acoustic properties (e.g., between fatty breast tissue and a fluid-filled cyst). Typically, a woman would lie in a supine position with her arm behind her head, and an ultrasound transducer is placed on her breast. Ultrasound accuracy is strongly dependent on the skill of the operator. No intravenous injections are necessary. For every 1,000 women who had a negative ultrasound test, about 950 women would have avoided an unnecessary biopsy, but 50 women would have missed cancers.
  • Positron emission tomography scanning (PET scan)—In PET scanning, a small amount of radioactive glucose is injected into the bloodstream. A gamma camera scanner, whole body scanner, or specific breast scanner are used for breast imaging to scan for the glucose uptake. Areas with rapid metabolism/high growth (i.e., tumors) will have a high amount of tracer uptake. For every 1,000 women who had a negative PET scan, about 924 women would have avoided an unnecessary biopsy, but 76 women would have missed cancers.
  • Scintimammography—Scintimammography is a nuclear medicine scan using 99mTc-sestamibi (most commonly) as a radioactive tracer injected into the bloodstream. A gamma camera scanner (for a 2-D planar image) or a single photon emission tomography (SPECT) scanner (for a 3-D image similar to CT scanning) is used to identify areas of high tracer uptake, indicative of a potential tumor. For every 1,000 women who had a negative scintimammogram, about 907 women would have avoided an unnecessary biopsy, but 93 women would have missed cancers.

The findings are calculated based on average risk for cancer, but risks for individual women may vary widely, based on factors such as age, family history and specific findings on mammogram or physical examination. The report says women who may wish to elect to have a noninvasive procedure should discuss their individual risk of cancer with their health provider.

"There is a wealth of information in this report that can give women and their health care providers detailed and helpful insight into the strengths and weaknesses of each of these techniques," Dr. Clancy said.

Although no accuracy rate is established as acceptable, the report cites a 2003 analysis by the Ontario Ministry of Health that concluded that an accuracy rate for negative findings of 98 percent or more (20 cancers missed per 1,000 women testing negative) would be an acceptable level to reliably preclude breast biopsy.

The report was carried out through systematic review of 81 studies by the ECRI Evidence-based Practice Center, Plymouth Meeting, PA. ECRI is one of 13 evidence-based practice centers carrying out effectiveness research for AHRQ's new Effective Health Care Program (http://www.effectivehealthcare.ahrq.gov). The program compares the effectiveness of different interventions, including drugs, in order to better inform consumers, health care providers and others as they make treatment choices.

The U.S. Preventive Services Task Force, supported by AHRQ, has made several recommendations regarding breast cancer screening. In particular, the Task Force recommends screening mammography, with or without clinical breast exam, every 1-2 years for women aged 40 and older. The Task Force's recommendations can be viewed at http://www.uspreventiveservicestaskforce.org/uspstf/uspsbrca.htm.

The report released today is available at http://www.effectivehealthcare.ahrq.gov. This Web site includes features for the public to participate in the Effective Health Care Program. Users can sign up to receive notification when new reports are available. They can also be notified when draft reports and other features are posted for comment, and comments can be submitted through the Web site. The public is also invited to use the Web site to nominate topics for review by the Effective Health Care Program. Copies of the executive summary of the report may be obtained by calling AHRQ's Publications Clearinghouse at (800) 358-9295 or sending an E-mail to AHRQPubs@ahrq.hhs.gov.

Editor's Note: AHRQ has produced an audio news release on this report that includes a soundbite from AHRQ Director Dr. Carolyn Clancy. You may download the .mp3 file or the transcript by visiting http://www.ahrq.gov/news/av.htm.

For more information, please contact AHRQ Public Affairs: (301) 427-1855 or (301) 427-1241.


 

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