99mTc-(V)DMSA scintimammography in the assessment of breast lesions: comparative study with 99mTc-MIBI

The purpose of this study was to evaluate and compare the diagnostic accuracy of pentavalent technetium-99m dimercaptosuccinic acid [99mTc-(V)DMSA] and 99mTc-methoxyisobutylisonitrile (MIBI) in the detection of primary breast cancer and metastatic lymph node involvement, and in the clarification of cases with indeterminate mammograms. Forty-one women (mean age±SD 55±7 years) referred for a suspicious breast lesion on physical examination and/or an abnormal mammogram underwent MIBI and (V)DMSA scintimammography (SMM) at separate sessions (48-h interval). Lateral prone and anterior supine images were obtained at 10 and 60 min after administration of 740–925 MBq of each tracer, in the arm contralateral to the breast lesion. The ipsilateral axillary region was also included in the field of view. The results of SMM and mammography were compared with histological findings. Breast cancer was histologically confirmed in 26 patients (mean diameter±SD 2.87±1.5 cm). Benign lesions were found in 15 patients (mean diameter±SD 2.04±2.7 cm). Mammography was definitely positive in 23/26 patients with breast cancer and indeterminate in 3/26 (sensitivity 88.4%). In benign lesions, mammography was true negative in 5/15 cases and indeterminate in 10/15 (specificity 33.3%). Both MIBI and (V)DMSA SMM detected 23/26 breast cancers (sensitivity 88.4%) and were true negative in 14/15 (specificity 93.3%). T/B ratios for breast cancer in MIBI and (V)DMSA scans were similar, and significantly higher than for benign lesions. MIBI correctly diagnosed 12/13 and (V)DMSA 11/13 cases in which the findings of mammography were indeterminate. In addition, (V)DMSA detected seven of eight cases of in situ ductal carcinoma (DCIS) associated with infiltrating carcinomas, while MIBI detected only two of these eight cases. (V)DSMA was also diffusely concentrated in benign lesions complicated by epithelial hyperplasia. Metastatic lymph node involvement was successfully imaged in 15/19 patients with metastatic disease by both agents (sensitivity 78.9%), while true-negative scans were observed in 19/22 (specificity 86.3%) patients with benign or malignant tumours without lymph node metastases. Linear regression analysis revealed a high coefficient of correlation between the (V)DMSA and the MIBI T/B ratios (r=0.8 P<0.001). We conclude that both (V)DMSA and MIBI show an excellent ability to detect breast cancer and its lymph node metastases. (V)DMSA also has a tendency to be diffusely and more intensely localised than MIBI in pre-invasive lesions, such as DCIS or epitheliosis, which are at risk of developing into malignancies. (V)DMSA could therefore provide a useful tool in the diagnosis of such lesions and possibly modify a predefined surgical plan. Finally, we believe that both tracers could offer an alternative method for elucidating non-diagnostic mammograms.