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Noninvasive tests may miss breast cancer
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 supported by the Agency for Healthcare Research and Quality (AHRQ).
The study is the second from AHRQ's new Effective Health Care Program, which compares the effectiveness of different treatments for health conditions. Researchers found 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 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. 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 (for example, 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 (such as 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 usually using 99mTc-sestamibi 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 indicates that women who wish to have a noninvasive procedure should discuss their individual risk of cancer with their health provider.
More details can be found in Effectiveness of Noninvasive Diagnostic Tests for Breast Abnormalities: Comparative Effectiveness Review, No. 2, by Wendy Bruening, Ph.D., Jason Launders, M.Sc., Nathan Pinkney, B.S., R.D.M.S., and others, Rockville, MD: Agency for Healthcare Research and Quality. February 2006. Available online at: http://www.effectivehealthcare.ahrq.gov/reports/final.cfm. Copies of the executive summary (AHRQ Publication No. 06-EHC005-1) of the report are also available from the AHRQ Clearinghouse.
Editor's Note: 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. 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 Effective Health Care Program Web site at http://www.effectivehealthcare.ahrq.gov 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. AHRQ has also produced an audio news release on this report that includes a soundbite from AHRQ Director Dr. Carolyn Clancy. A transcript and soundbite, an .mp3 file, may be downloaded by visiting http://www.ahrq.gov/news/av.htm.
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