CHICAGO--Scintimammogra-phy, a nuclear medicine procedure developed in the early 1990s, has potential as a diagnostic tool for identifying breast cancer in women whose disease hides within dense tissue, said Janet Baum, MD, a radiologist at New England Deaconess Hospital, Boston.
In a preliminary trial at 42 medical centers, Tc-99m sestamibi breast imaging was equally accurate at predicting malignancies in dense breasts and in fatty breasts. Sestamibi breast imaging had high positive and negative predictive values for cancer that were not affected by breast density, Dr. Baum reported at the annual meeting of the Radiological Society of North America (RSNA).
Dr. Baum also suggested that Tc-99m sestamibi breast imaging might refine biopsy protocols by eliminating the routine practice of sampling all palpable breast nodules when a significant number turn out to be benign.
However, Edward Sickles, MD, chief of mammography, University of California, San Francisco, expressed concern that the sensitivity of sestamibi breast imaging "didn't come close to the 95% to 98% level we generally require to call a lesion exempt from biopsy."
Sensitivities achieved with scintimam-mography were no higher than 82% for palpable and nonpalpable lesions. "It is dangerous to eliminate a biopsy when your own accuracy is not even 90%," Dr. Sickles said.
The multicenter trial included 563 women, 315 with palpable nodules and 248 with nonpalpable mammographic abnormalities. Women were classified as having fatty breasts if mammography showed tissue that was composed almost entirely of fat or contained numerous vague densities. Women were considered to have dense breasts if mammography showed extremely or heterogeneously dense tissue.
Forty-eight percent of the women with palpable lesions had a malignancy at biopsy. Scintimammographic findings in these women were equally sensitive to breast cancer in dense tissue (80% sensitivity) and fatty tissue (79% sensitivity).
Overall accuracy for sestamibi breast imaging was 79% for palpable nodules and 80% for nonpalpable abnormalities. Both positive and negative predictive values were similar for women with palpable lesions (77% and 82%, respectively) and nonpalpable lesions (76% and 81%, respectively).
Scintigraphic findings could contribute to the decision to biopsy rather than follow. When mammography of a woman with extremely dense breasts showed only microcalcifications in the upper inner quadrant of the left breast corresponding to a palpable nodule, scin-timammography revealed increased Tc-99m sestamibi uptake indicative of tumor in that area. Scintimammography also detected lesions as small as 6 mm.
"Sestamibi showed good overall diagnostic accuracy, and it was independent of breast density," Dr. Baum said. "It therefore may make a useful contribution to a balanced breast evaluation program that includes mammography, magnetic resonance (MR) imaging, and ultrasound."
She said that sestamibi imaging should be considered as part of the diagnostic armamentarium to evaluate breasts that are mammographically difficult to image, "particularly when the ultrasound capability in an institution is not as good as you would like or a patient cannot have an MR or MR is not available."
DuPont Pharma Radiopharmaceuticals, a division of the DuPont Merck Pharmaceutical Company, which sponsored the research, has filed a supplemental New Drug Application for use of Tc-99m sestamibi for breast imaging. The product is currently marketed for use in heart imaging.
