Molecular Breast Imaging in Patients with Suspicious Calcifications

Objective We evaluated the accuracy of molecular breast imaging (MBI)—a nuclear medicine technique that employs dedicated dual-detector, cadmium zinc telluride gamma cameras to image the functional uptake of a radiopharmaceutical (typically Tc-99m sestamibi) in the breast—in patients with suspicious calcifications on mammography. Methods Women scheduled for stereotactic biopsy of calcifications detected on 2D digital mammography were prospectively enrolled to undergo MBI before biopsy. Molecular breast imaging was performed with injection of Tc-99m sestamibi and a dual-detector, cadmium zinc telluride gamma camera. Positive findings on either modality were biopsied. High-risk and malignant biopsy findings were excised. Results In 71 participants, 76 areas of calcifications were recommended for biopsy after mammography, and 24 (32%) were malignant, including 20 cases of ductal carcinoma in situ (DCIS) and 4 cases of invasive ductal cancer. Prebiopsy MBI was positive in 17 of the 76 (22%) calcifications, including 10 of 20 (50%) DCISs and 2 of 4 (50%) invasive cancers. The median pathologic size for MBI–positive cancers was 1.5 cm (range 0.5–3.2 cm) compared with 0.9 cm (range 0.1–2.0 cm) for MBI–negative cancers (P = 0.09). Non-mass uptake on MBI led to additional biopsies of 6 sites in 6 patients, and 2 of 6 (33%) MBI–detected incidental lesions showed malignancy; both DCIS contralateral to the mammographically detected calcifications. The overall per-lesion positive and negative predictive values of MBI in this prebiopsy setting were 61% (14 of 23) and 80% (47 of 59), respectively. Conclusion Molecular breast imaging has insufficient negative predictive value to identify calcifications in which biopsy could be avoided. However, among women presenting for biopsy of suspicious calcifications, MBI revealed additional sites of mammographically occult breast cancer. To avoid biopsy of suspicious calcifications on mammography, negative findings on MBI should not be used.