Scintimammography Detects Tumors in Dense Breast Tissue

NEW ORLEANS—Scintimam-mography utilizing a radionuclide already approved by the FDA for cardiac imaging has been shown to compare favorably with standard mammography in a new study presented at the 99th annual meeting of the American Roentgen Ray Society.

Conducted by Michael A. Blake, MD, (currently a fellow in body imaging at Brigham and Women’s Hospital, Boston) and his colleagues (Drs. C. Williams, E. McDermott, and G. Duffy at St. Vincent’s and St. Anne’s Hospitals, Dublin, Ireland), the study prospectively compared technetium tetrofosmin scintimammog-raphy with conventional mammography. The results showed the new technique to be especially useful in women with dense breasts.

Another radionuclide, technetium sestamibi, is already in use for breast scin-timammography. “Technetium tetrofosmin is similar in uptake and localization to sestamibi, but tetrofosmin is much easier to prepare,” Dr. Blake said.

The study population was composed of 106 women with clinically or mam-mographically detected abnormalities that warranted biopsy. Each woman underwent both technetium tetrofosmin scintimammography and conventional mammography prior to biopsy, and the imaging results were correlated with pathologic outcome.

“Conventional mammography is problematic in women with dense breasts or where there is architectural distortion due to prior surgery and scarring,” Dr. Blake explained. And scintimammog-raphy does not require breast compression, he added.

In this technique, images are taken for 10 minutes each in prone lateral and anterior supine positions, beginning 10 minutes after intravenous injection of the radionuclide. The injection is well tolerated by patients.

Sensitivity and Specificity

The sensitivity of scintimammography was a bit lower than that of conventional mammography, 79.1% vs 85.7%, respectively; but scintimammography scored much better than conventional mammography on specificity, accuracy in distinguishing benign from malignant lesions, and positive predictive value. The negative predictive value (84.1%) of scintimammography was about the same as that of conventional mammography (81.6%).

Most of the false-positive scintimam-mograms were due to highly cellular benign conditions, such as fibroadenoma, whereas the false-negative scans were mostly due to small tumors, Dr. Blake pointed out.

Scintimammography was especially valuable in detecting malignancies in dense breast tissue. The four cancers detected by scintimammography but missed by conventional mammography were all in dense breasts.

Detecting Positive Nodes

Nodal involvement was studied in 23 cases, 13 of which were found to have metastatic nodal involvement at biopsy. Scintimammography detected 9 of the cases with malignant lymph nodes, with only one false-positive result, he said.

Dr. Blake indicated that technetium tetrofosmin scintimammography had 91.9% accuracy in distinguishing benign from malignant lesions, but he emphasized that it is a complementary technique to conventional mammography, and is not a replacement for other complementary techniques.

The technique can help doctors target the most appropriate area for biopsy, or it can help reduce biopsies by differentiating scar tissue.

“There are occasions when something looks bad on mammogram, but with the help of this test, it proves to be just a scar from previous surgery, for example,” Dr. Blake said.

He also noted that their findings in the small sample of patients with nodal involvement suggest another promising area for research.