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NATIONAL HARBOR, Md. -- Breast-specific gamma imaging (BSGI) outperformed breast ultrasound for evaluating patients with indeterminate mammograms in a retrospective comparison of the two imaging techniques, researchers reported here.

In an evaluation of more than 100 mammograms, BSGI showed a 100% sensitivity and 80% specificity. In contrast, breast ultrasound had a sensitivity of 47% and specificity of 67%, according to a study by Anne L. Rosenberg, MD, of Thomas Jefferson University in Philadelphia, and colleagues.

BSGI also demonstrated better accuracy for identifying malignancies, high-risk lesions, and benign lesions, Rosenberg said during a poster presentation at the American Society of Clinical Oncology's Breast Cancer Symposium.

"In this study we demonstrated that BSGI is more sensitive and more specific than ultrasound," Rosenberg told 番茄社区. "While it called some cases positive that were benign, it didn't miss any of the cancers, and it called fewer of the benign things positive than ultrasound did," she explained in an interview.

Up to 10% of mammograms yield indeterminate results, often because dense breast tissue can be difficult to image.

Breast ultrasound or MRI can be used to clarify the findings, particularly when indeterminate mammograms are associated with unexplained signs or symptoms, such as breast pain, nipple discharge, or a palpable mass.

BSGI offers a potential alternative to ultrasound or MRI for breast evaluation following indeterminate mammography. Gamma imaging is less time consuming and more "patient friendly" compared with MRI and more cost competitive with ultrasound, said Rosenberg.

Few studies have compared the overall utility of BSGI and ultrasound for resolving indeterminate mammograms. To address this lack of data, Rosenberg and colleagues retrospectively compared findings with BSGI and breast ultrasound in 111 women with indeterminate mammograms.

The same radiologist reviewed all imaging studies and classified breast tissue according to Breast Imaging and Reporting Data System (BIRADS) criteria as fatty (BIRADS density 1 or 2) or dense (BIRADS density 3 or 4). Imaging studies were classified as positive (BIRADS IV or V), negative (BIRADS I or II), or indeterminate (BIRADS 0 or III).

Biopsy results served as the gold standard for characterizing breast lesions, which were classified as malignant, high-risk (atypical ductal or lobular hyperplasia or lobular carcinoma in situ), or benign.

Pathology identified 94 lesions as benign, four as high risk, and 17 as malignant. Ultrasound led to characterization of 12 lesions as negative (all benign), 39 as positive (31 benign, seven malignant, and one high risk), and 60 still indeterminate (51 benign, six malignant, and three high risk).

BSGI results were negative in 45 cases (all benign), positive in 36 cases (19 benign, four high risk, and 13 malignant), and indeterminate in 30 cases (all benign).

"For these patients with indeterminate mammograms, breast ultrasound also was indeterminate more than half of the time," Rosenberg said. "Of the 60 indeterminate ultrasound studies, BSGI identified malignancies in six cases and high-risk lesions in three."

If patient management had been based solely on imaging results, BSGI would have led to incorrect management in fewer than 20 patients compared with more than 30 with breast ultrasound. BSGI would have led to correct management in more than half of the patients compared with about 20% with ultrasound.

Equating indeterminate imaging results with no change in management, Rosenberg said the designation would have applied to 30 cases with BSGI and 60 with ultrasound.

Some concern has arisen regarding the potential risk associated with radiation exposure with BSGI, which requires an intravenous radiopharmaceutical. Investigators addressed the concern with a risk/benefit analysis of the 111 patients.

BSGI detected 13 malignancies, accounting for 11.7% of the patients and translating into a benefit ratio of 0.117. Each BSGI study required 20 mCi of technetium-99m sestamibi, a dose associated with a hazard rate of 37.2 cancers per 100,000 cases, or a risk ratio of 0.000372.

"Therefore, the benefit to this group of patients is 295 times greater than the risk," Rosenberg and colleagues concluded in their poster presentation. "BSGI is a safe diagnostic imaging procedure resulting in radiation exposure similar to other diagnostic imaging studies."

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