Molecular breast imaging may be a more cost-effective follow-up approach to mammography than MRI for high-risk women and those with dense tissue, according to a small retrospective study. The two imaging techniques had a sensitivity exceeding 90% and specificity of about 50%, Carrie B. Hruska, Ph.D., of the Mayo Clinic in Rochester, Minn., reported at the Era of Hope meeting here, sponsored by the Department of Defense Breast Cancer Research Program.
Although mammography remains a reliable screening and diagnostic test for breast cancer, the imaging technique has reduced sensitivity in some high-risk women and those with dense breast tissue. Increasingly, breast MRI is being used in women who are not well served by mammography, said Dr. Hruska.
However, the high cost of MRI and need for a high level of interpretative expertise prohibit routine use for breast evaluation.
Molecular breast imaging, a nuclear medicine technique, employs specialized gamma cameras to detect the preferential uptake of the radiotracer technetium-99 sestamibi in breast disease, said Dr. Hruska. The imaging technique's accuracy is unaffected by breast-tissue density and costs a quarter to a sixth of a bilateral breast MRI. Moreover, interpretation of molecular breast imaging exams is considerably less complex compared with MRI. Given the potential advantages of molecular breast imaging, Dr. Hruska and colleagues retrospectively reviewed records of 48 women who had both breast MRI and molecular breast imaging within a 30-day period. Six patients had screening MRI because of increased risk for breast cancer and the remaining 42 had MRI to evaluate areas of concern left unresolved by mammography or to determine disease extent. Imaging accuracy was determined by biopsy results or by follow-up status at 15 months for women who did not undergo biopsies. Subsequently, 54 malignancies were diagnosed in 32 patients, 15 of them with multifocal or multicentric disease. MRI detected 53 of 54 lesions in 31 patients for a sensitivity of 98% compared with 94% for molecular breast imaging, which detected 51 of 54 cancers in 30 patients. MRI led to correct characterization of nine of 16 true-negative results specificity, and molecular breast imaging ruled out cancer in eight of the 16 cases. False-positive results with MRI led to further evaluation of 12 patients with MRI and to nine biopsies of benign lesions. False-positives with molecular breast imaging prompted evaluation of 11 patients and seven biopsies of benign lesions.
MRI and molecular breast imaging interpretations were concordant for the presence of disease and number of cancer foci in 47 of 48 patients. The single case of discordance occurred in a patient whose MRI exam identified two cancer foci that were missed by molecular breast imaging.