Researchers at the Legacy Good Samaritan Hospital in Portland, Oregon presented data on the clinical use of Breast-Specific Gamma Imaging (BSGI), a molecular breast imaging technique, at the American Society of Breast Surgeons Annual meeting in Las Vegas in April: Breast Specific Gamma Imaging Used As An Adjunct to Mammography.
664 patients were involved in the retrospective review where BSGI was evaluated as part of the diagnostic work-up of patients that had presented with abnormal mammographic orultrasound imaging, physical exam, significant family or personal breast cancer history or dense breasts. Overall, the sensitivity was 85 percent with a specificity of 81 percent. The positive predictive value (PPV) was 68 percent and the negative predictive value was 81 percent. Using the Breast Imaging Reporting and Data System (BI-RADS), the PPV for BI-RADS 1-3 of 30% compares favorably with the expected BI-RADS prediction of <2 percent malignancy rate for this category. In the BI-RADS 4-6 group, the PPV increased considerably to 86%.
Dr. Nathalie Johnson, Medical Director of Cancer Services at Legacy Good Samaritan Hospital, and principal investigator on the study, concluded, "BSGI is a useful adjunct in the imaging work-up of breast patients and has a high sensitivity and specificity. It is best used to further evaluate unclear mammographic or ultrasound findings, as the positive predictive value is highest in this setting. However, in high-risk patients with BI-RADS 1-3, it will improve cancer detection significantly."
Overall, mammography and BSGI were both positive in 144 cancers. BSGI was positive in 23 cancers which were negative by mammography. However, there were 26 cancers positive on mammography and negative on BSGI. In short, BSGI can improve breast cancer detection in patients with normal or indeterminate mammograms, but should not be used to obviate the need for biopsy in patients with positive mammographic findings.
For the study, BSGI was conducted using a Dilon 6800®, a digital high-resolution, breast-optimized gamma camera. With BSGI, the patient receives a pharmaceutical tracing agent that is absorbed by all the cells in the body. Due to their increased rate of metabolic activity, cancerous cells absorb a greater amount of the tracing agent than the normal surrounding tissue and generally appear as dark spots on the BSGI image.