Role of 99mTc-MIBI in evaluation of palpable breast lesions

Full text: Breast carcinoma is the most frequently diagnosed malignancy in women with 41% of all new cases diagnosed in developing countries. Over 323,000 women in the developing countries were detected in 1990, leading to 140,000 deaths. The annual incidence of breast carcinoma among women in Pakistan accounts for 32% of all detected carcinomas and 18% of all cancer related deaths. Three years data (2000-2002) collected from Bahawalpur Institute of Nuclear Medicine and Oncology (BINO) indicated that 16.5% of the total patients were registered with carcinoma breast. To reduce the mortality associated with this disease, screening of asymptomatic women has been advocated to diagnose problems at an early stage, particularly by X-ray mammography on annual basis after the age of 50. The available imaging modalities like mammography and ultrasound lack the desired specificity to differentiate the malignant masses from benign ones; hence there is a need to search for more specific imaging tool and to save the patients from unnecessary biopsies. Technetium-99m labeled methoxy-isobutyl-isonitrile (99mTc-MIBI) is a well-known cardiac perfusion-imaging agent. After convincing reports from various parts of the world that it specifically accumulates in malignant breast masses, we carried out a study to evaluate the diagnostic performance of 99mTc-MIBI scintimammography in palpable breast lesions. Patients with palpable breast lesions were studied after obtaining informed written consent. The study was carried out as a prospective trial. A total of 42 patients with 45 palpable breast masses were included in this study. The median age was 44 years (range 19-84 years). Tc-99m-MIBI was injected in a dose of 740 MBq in dorsal pedal vein and if unsuccessful then in medial cubital vein on the opposite side of the breast, to be imaged for the lump. Planar 10 minutes images in prone lateral and in supine position with arms raised behind the head were acquired 10 minutes and 60-90 minute post injection. A positive result for malignancy was defined as one or more focal areas of increased tracer uptake in both early and delayed images. A benign lesion was considered as mild focal or diffuse tracer uptake in the early image with tracer washout in the delayed image. Histopathology revealed 29 malignant and 16 benign pathologies. Among the malignant group, there were 24 invasive ductal carcinoma, 3 invasive lobular carcinoma, one undifferentiated, and one metastatic carcinoma. Of the benign group 7 were of fibroadenoma, 4 fibrocystic changes and 5 had inflammatory lesions. Tumor size ranged from 0.8 cm to 8.0 cm with a median value of 3.5 cm. Scintigraphy was true positive in 27 of 29 malignant lesions. In the benign group, results were true negative in 16 of 16 cases. Sensitivity and specificity has been calculated to be 93.10% and 100%. Of the 02 false-negative results, we found one case of undifferentiated carcinoma and the other one of metastatic carcinoma. There were no false-positive results. In the light of this study we conclude that 99mTc-MIBI scintimammography has a promising role in breast cancer detection with significant diagnostic accuracy in terms of sensitivity and specificity in cases of palpable breast lumps. This test reduces a great deal of unnecessary breast biopsies. (author)