AJR: Molecular breast imaging outperforms ultrasound
Molecular breast imaging techniques, such as breast-specific gamma imaging, have been developed partially to help address the limitations of screening mammography and ultrasound: relatively low positive predictive value and sensitivity. Previous studies had estimated the sensitivity and specificity of breast-specific gamma imaging at 89 to 96 percent and 65 to 90 percent, respectively.
Jean M. Weigert, MD, of the department of radiology at Mandell and Blau MDs in New Britain, Conn., and colleagues sought to quantify the impact of breast-specific gamma imaging in clinical practice and identify patients who benefit from the modality.
The researchers analyzed 1,042 women included in a multicenter patient registry who underwent breast-specific gamma imaging.
Patients were recommended for the molecular imaging exam based on one or more of the following indications: equivocal mammography or ultrasound findings, personal history of breast cancer, family history or other risk factors establishing high risk for breast cancer, recent positive mammogram, clinical finding or dense breast tissue.
Radiologists used all imaging data as well as patient history to interpret the imaging studies and determine patient management. Biopsy, when performed, or imaging follow-up served as the reference standard.
Among the 1,042 women in the registry, biopsy or follow-up resulted in 250 positive and 792 negative findings. Weigert and colleagues calculated that breast-specific gamma imaging had an overall sensitivity, specificity, positive predictive value and negative predictive value of 91 percent, 77 percent, 57 percent and 96 percent, respectively.
When the researchers analyzed data by subgroups based on BI-RADS categories, they found the improvement compared with mammography and ultrasound was most apparent in patients with a BI-RADS category 0 mammogram. “For this group of patients, breast-specific gamma imaging was significantly more likely to contribute to patient management than ultrasound (109 vs 71 patients) and it was less likely to be negative in malignant lesions (three vs zero). In addition, breast-specific gamma imaging was less likely to be positive in benign lesions,” wrote Weigert et al.
Overall, breast-specific gamma imaging provided information that resulted in a change in management for more patients (156 vs 113) than ultrasound, while also delivering improved specificity and positive predictive value.
The researchers noted that for women with a positive finding on mammography, ultrasound and breast-specific gamma imaging have a false-negative rate of 6 percent and 8 percent, respectively. Those rates do not obviate the need for a biopsy. “There may still be a role for these adjunctive procedures in treatment planning, such as determining the extent of the primary lesion and detecting additional disease occult by mammography.”
Weigert and colleagues noted some limitations to the study, which was a retrospective analysis without a control group. The follow-up period at a minimum of six months after enrollment provided limited evidence of the lack of malignancy. Finally, because breast-specific gamma imaging was recommended after mammography and ultrasound, the cohort may have been biased toward patients with difficult to interpret or discordant studies.