Objective: To determine the sensitivity of molecular breast imaging (MBI) to detect small cancers of the breast.
Patients and methods: A cadmium-zinc-telluride gamma camera with a field of view of 20 x 20 cm was used. The detector elements were 2.5 x 2.5 mm. The gamma camera was mounted on a modified mammographic gantry. Between November 2001 and March 2004, we performed MBI on patients who were scheduled to undergo biopsy for a lesion suggestive of malignancy that was smaller than 2 cm on a mammogram. Patients were injected with 20 mCi of technetium Tc 99m sestamibi and underwent imaging immediately after injection. Using light pain-free compression, we obtained craniocaudal and mediolateral oblique views of each breast.
Results: Of the 40 women included in the study, 26 had a total of 36 malignant lesions confirmed at surgery. Of these 36 lesions, 33 were detected by MBI (overall sensitivity, 92%). Of the 22 malignant lesions 1 cm or smaller in diameter, 19 were detected by MBI (sensitivity, 86%). Two patients had false-negative MBI results. Of the 14 malignant lesions larger than 1 cm in diameter, all were identified correctly by MBI. In 4 patients, MBI identified additional lesions not seen on mammography that were confirmed subsequently on magnetic resonance imaging and were true-positive cases at surgery. Three of these patients had lesions in the breast contralateral to the breast containing the initial mammographic finding suggestive of malignancy. Of 14 patients with no evidence of cancer at biopsy or surgery, 9 had true-negative (normal) scans and 5 had false-positive scans on MBI. False-positive results included benign fibroadenoma (2 patients), inflammatory fat necrosis (1 patient), benign breast parenchyma (1 patient), and complex sclerosing lesion (1 patient).
Conclusion: This prototype gamma camera system for MBI reliably detects malignant breast lesions smaller than 2 cm. Furthermore, we obtained the highest sensitivity (86%) yet reported for the detection of lesions smaller than 1 cm. These results suggest an important role for MBI, particularly for women in whom the sensitivity of mammography is reduced by the density of the breast parenchyma.