Dedicated Dual-Head Gamma Imaging for Breast Cancer Screening in Women with Mammographically Dense Breasts

PURPOSE: To compare performance characteristics of dedicated dual-head gamma imaging and mammography in screening women with mammographically dense breasts. MATERIALS AND METHODS: Asymptomatic women (n = 1007) who had heterogeneously or extremely dense breasts on prior mammograms and additional risk factors provided informed consent to enroll in an institutional review board-approved HIPAA-compliant protocol. Participants underwent mammography and gamma imaging after a 740-mBq (20-mCi) technetium 99m sestamibi injection. Reference standard (more severe cancer diagnosis or 12-month follow-up findings) was available for 936 of 969 eligible participants. Diagnostic yield, sensitivity, specificity, and positive predictive values (PPVs) were determined for mammography, gamma imaging, and both combined. RESULTS: Of 936 participants, 11 had cancer (one with mammography only, seven with gamma imaging only, two with both combined, and one with neither). Diagnostic yield was 3.2 per 1000 (95% confidence interval CI: 1.1, 9.3) for mammography, 9.6 per 1000 (95% CI: 5.1, 18.2) for gamma imaging, and 10.7 per 1000 (95% CI: 5.8, 19.6) for both (P = .016 vs mammography alone). One participant had a second ipsilateral cancer detected with gamma imaging only. Prevalent screening gamma imaging demonstrated equivalent specificity relative to incident screening mammography (93% 861 of 925 vs 91% 840 of 925, P = .069). Of eight cancers detected with gamma imaging only, six (75%) were invasive (median size, 1.1 cm; range, 0.4-5.1 cm); all were node negative. The ratio of the number of patients with breast cancer per number of screening examinations with abnormal findings was 3% (three of 88) for mammography and 12% (nine of 73) for gamma imaging (P = .01). The number of breast cancers diagnosed per number of biopsies performed was 18% (three of 17) for mammography and 28% (10 of 36) for gamma imaging (P = .36). CONCLUSION: Addition of gamma imaging to mammography significantly increased detection of node-negative breast cancer in dense breasts by 7.5 per 1000 women screened (95% CI: 3.6, 15.4). To be clinically important, gamma imaging will need to show equivalent performance at decreased radiation doses.