In a study published in the Journal of Nuclear Medicine, Dr. Johannes Czernin of the University of California, Los Angeles and colleagues published preliminary results that positron emission tomography (PET) may be more accurate than conventional imaging tests for determining if breast cancer has spread in women who have been previously treated for the disease.

Czernin's team evaluated a specific type of PET called FDG PET, which measures how much glucose (sugar) is being used by breast tissues. A higher level of the sugar molecule uptake indicates that these cells may have higher energy requirements, a characteristic of many cancer cells.

In effect, the PET technique measures the "living chemistry" of a tumor, instead of just a fixed image. It looks at the activity going on within tissues rather than just at the tissues themselves. This can often provide a better indication of whether a malignancy is present.

The researchers studied 61 women who had undergone both PET and a combination of conventional imaging tests after being treated for breast cancer. These tests included mammography, CT scans, magnetic resonance imaging (MRI) and ultrasound. After a six month follow-up period, they found that the results of PET and the conventional imaging techniques were in agreement for three-quarters of the women.

However, for a quarter of the women, the results were contradictory. For nine of the women, PET showed that cancer had returned, but there were negative results on the conventional imaging tests. Conversely, for six of the women, the PET results were negative, but conventional testing showed that cancer had returned.

When the researchers further evaluated these contradictory results, PET turned out to be correct in 12 of the 15 cases, while conventional imaging was correct in only 3 of the 15 cases.

"FDG PET can be used to improve prediction of the clinical outcome of previously treated breast cancer patients relative to what is achievable through conventional imaging alone," the researchers concluded. However, these results must first be confirmed by much larger studies, and current guidelines do NOT recommend its routine use for screening after completion of adjuvant therapy.

SOURCE:
Journal of Nuclear Medicine, March 2002; 43:325-329