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A new study suggests that the PET scan may be more beneficial in determining whether breast cancer has returned after treatment than conventional imaging tests, such as mammography, CT scan, or ultrasound. PET (positron emission tomography) is a type of nuclear medicine imaging that involves injecting a patient with a radioactive substance and then analyzing how the substance is absorbed by certain tissues. The publication of the study comes shortly after Medicare announced that it will cover the cost of PET scans for women who have been treated for breast cancer. To date, PET has not been commonly used to detect breast cancer because few studies have shown it to be comparable to other diagnostic/follow-up tests. While this new study will not propel PET into mainstream use on breast cancer patients, it adds to a growing number of small studies that show PET has potential to be a useful supplement in helping to monitor breast cancer recurrences. Nuclear medicine studies have been used since the 1950s to help detect disease in several body areas, including the brain, heart, and lungs. Nuclear medicine studies require the use of very low-level radioactive chemicals called radionuclides, radiopharmaceuticals or radiotracers. These radioactive substances are specially formulated to collect temporarily in the specific part of the body being studied. After the substance has entered the body, a gamma camera is used to capture radiation signals emitted from the body area. The signals are then reconstructed and displayed on a computer monitor for physician analysis. PET is one type of nuclear medicine test that involves cross sectional data acquisition and reconstruction similar to the CT (computed tomography, or CAT) scan. Another type of nuclear medicine imaging called scintimammography is also used on a limited basis to help detect breast cancer and/or monitor treatment. To determine whether full-body PET scan (or FDG PET) is useful at detecting cancer recurrences in women who have been treated for breast cancer, lead researcher Duska Vranjesevic, MD of UCLA School of Medicine in Los Angeles, California and his team analyzed PET scan results of 61 breast cancer patients. FDG PET measures the amount of glucose, or sugar, in cells to identify cancer and determine whether it has spread to other body parts (cancer cells tend to absorb more glucose than normal cells). All of the women in the study also underwent conventional imaging (CT, MRI, mammography, etc.) as a comparison to PET. After six months of follow-up, Dr. Vranjesevic and his colleagues found that PET imaging was superior to conventional imaging at detecting breast cancer (or determining that cancer was not present). In one-fourth of the women in the study, PET and conventional imaging tests produced contradictory results. Among these cases, PET did not suggest cancer in six women that had positive conventional imaging test results (i.e., the conventional tests indicated cancer). Also, PET produced positive results in six of nine women whose conventional imaging tests did not indicate cancer. Among the contradictory cases, the researchers found the PET results to be accurate in 80% of the cases while conventional imaging was accurate in only 20% of the cases. According to Dr. Vranjesevic and his team, PET may be more accurate than conventional imaging tests that sometimes mistake inflamed (swelled) tissue or scar tissue as breast abnormalities. PET may also detect some cancerous tumors that conventional imaging tests are unable to find. On the other hand, PET can also provide relief to a patient whose cancer has not recurred, according to co-researcher Johannes Czernin, MD. However, as with many studies on diagnostic imaging tests, the researchers caution that the results of their study must be confirmed in additional trials to determine whether PET offers true advantages over conventional imaging tests in detecting breast cancer recurrence. Furthermore, while nuclear medicine tests can be useful in certain situations (such as detecting a breast cancer recurrence, as this study suggests), they are not used as a primary investigative tool for breast cancer. Mammography, which involves creating special x-ray images of the breasts, is currently the "gold standard" in breast cancer detection and the most commonly used diagnostic test to evaluate breast abnormalities. Another type of nuclear medicine breast imaging called scintimammography also involves analyzing the absorption of a radioactive substance in different tissues to determine whether breast cancer is present. Nuclear medicine breast imaging may be appropriate in the following situations:
Dr. Czernin believes that PET may also be useful in detecting first-time breast cancers in women who have breast implants or scars that tend to make mammography harder to interpret and thus less accurate.
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