Non-Invasive Diagnostic Tests Can't Replace Invasive Biopsy

Reviewed study: "Non-Invasive Diagnostic Tests Can't Replace Invasive Biopsy" by W. Bruening and others, Agency for Healthcare Research and Quality Report No. 06-EHC005-1, February 2006

Is this for me? If you want to know if ultrasound, MRIs, or other non-invasive diagnostic tests could be used instead of surgery (surgical or needle biopsy) to diagnose breast cancer, then you might want to read this article.

Background and importance of the study: Mammograms are probably the most important tool doctors have to help them diagnose, evaluate, and follow women who may currently have or may have already had breast cancer. Safe and highly accurate, a mammogram is an X-ray photograph of the breast. The technique has been in use for decades. But mammograms aren't perfect. Normal breast tissue can hide a breast cancer, so that it doesn't show up on the mammogram (the cancer is there but not found). This is called a false negative. And mammography can identify an abnormality that looks like a cancer but turns out to be normal. This "false alarm" is called a false positive.

If your mammogram shows an abnormality, your doctor will then order one or more additional diagnostic tests to determine whether the abnormality is a cancer or a false positive.

There are many different types of diagnostic tests available, including:

• Biopsy—a very small operation that removes tissue from an area of concern in the body. Cells from the tissue are then examined under a microscope to determine if cancer cells are present.
• MRI (magnetic resonance imaging)—uses magnetic fields, not radiation, to create images of the body. An injection of a special substance, gadolinium, is used during the scan to make it easier to find the cancer. The gadolinium makes the cancer "light up" in contrast to the normal tissue around it. A highly trained expert reads the results to determine if cancer might be present.
• Ultrasound—sends high-frequency sound waves through your breast and converts them into images on a viewing screen. Ultrasound is the best way to find out if an abnormality is solid or fluid-filled. But ultrasound can't determine if a solid lump is normal or cancerous.
• PET (positron emission tomography) scanning—a small amount of radioactive sugar is injected into the body. Active cells take up the radioactive sugar, and this helps radiologists identify areas where cells are overactive, which can indicate cancer.
• Scintimammography—as in a PET scan, a small amount of radioactive material is injected into the body. Normal breast cells take up little of the radioactive material, while active cells take up more, which can indicate cancer.

Each test has strengths and weaknesses.

A biopsy is an invasive test because a small portion of tissue is removed. MRI, ultrasound, PET scanning, and scintimammography are non-invasive tests because no tissue is removed.

In this study, researchers in the Agency for Healthcare Research and Quality (a division of the U.S. Department of Health and Human Services) wanted to know if non-invasive tests could accurately detect whether an abnormality on a mammogram is normal or cancerous. This would allow women with false positives to avoid biopsy.

Study design: In this study, the researchers performed a meta-analysis. A meta-analysis is a statistical way of combining the results of a group of studies on the same subject. These researchers combined the results of 81 studies that looked at the accuracy of:

• MRI,
• ultrasound,
• PET scanning, or
• scintimammography

for diagnosing breast cancer in women.

For each test, the researchers looked at:

• sensitivity—the probability that a test could detect a cancer in a woman with cancer, (known as "true-positives") and
• specificity—the probability that the test would show no cancer (be negative) in a woman without cancer, (known as "true-negatives").

The researchers also looked at the strengths and weaknesses of each test.

Results: To compare the accuracy of each test, the researchers reported their findings per thousand women who have an average risk of breast cancer.

• MRI: For every 1,000 women who had a negative MRI, about 962 women would have true negative results (no biopsy needed), but 38 women would have false negatives (their cancers would be missed).
• Ultrasound: for every 1,000 women who had a negative ultrasound, about 950 would have true negative results, but 50 would have false negatives.
• PET scan: for every 1,000 women who had a negative PET scan, about 924 women would have true negative results, but 76 would have false negatives.
• Scintimammography: for every 1,000 women who had a negative scintimammogram, about 907 women would have true negative results, but 93 would have false negatives.

Conclusions: The researchers concluded that, although all of the tests could reduce the need for biopsy in women with abnormal mammograms who do not have a cancer, each test would miss some cancers. None of these tests were considered accurate enough to replace biopsy.

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