The main purpose of this study was to compare the utility of technetium-99m methoxyisobutylisonitrile (Tc-99m sestamibi) scintimammography with that of ultrasonography for diagnosis of breast cancer in 32 female patients with indeterminate mammographic probability of malignancy because of mammographically dense breast. All breast masses were removed and histopathological diagnosis was obtained in all cases. The results showed 20 of 24 cases of breast carcinoma detected on Tc-99m sestamibi scintimammography. Only one out of eight patients with benign breast lesion had abnormal scintimammographic finding. Ultrasonography diagnosed 22 of the 24 cases of breast carcinoma. However, five out of eight patients with benign breast lesion had positive ultrasonographic findings. In differentiating malignant and benign breast tumors in mammographically dense breast, the diagnostic sensitivities were 83 and 92%, specificities were 88 and 38%, and accuracies were 84 and 78% for Tc-99m sestamibi scintimammography and ultrasonography, respectively. Ultrasonography showed a nonsignificantly higher sensitivity (p<0.05), but lower specificity, with more false-positive diagnoses made on ultrasonography. Due to its higher sensitivity, ultrasonography is more suitable for screening breast masses. However, Tc-99m sestamibi scintimammography exhibited significantly higher specificity (p<0.05) and accuracy in detecting malignant breast tumors in the current study. We conclude that Tc-99m sestamibi scintimammography is a safe and useful diagnostic method for detection of breast cancer in patients with nondiagnostic mammogram because of mammographically dense breast.
