The use of thallium-201 in the preoperative detection of breast cancer: an adjunct to mammography and ultrasonography. 
Thallium-201 breast scans were performed preoperatively in 72 female patients with breast abnormalities detected by mammography and/or ultrasonography (7.5-13 MHz), in order to differentiate benign from malignant breast disease.  Informed consent was obtained from each patient.  Scintigraphy consisted of anterior and oblique planar images of the affected breast and axilla at 10 min and 3 h following the injection of 201Tl chloride (110 MBq).  All 201Tl scans were interpreted without prior knowledge of surgery data.  Pathological features of breast malignancies, such as tumour size, axillary lymph node metastases, tumour grading, lymphatic vascular channel invasion and receptor status, were analysed for their association with 201Tl uptake by tumour cells.  A total of 76 breast lesions were assessed in the study.  On final histological diagnosis, there were 56 malignant tumours, 14 benign nodules (9 fibroadenomas, two cases of adenosis, two cases of focal fibrosis and one case of epitheliosis) and six atypical lesions (atypical ductal or lobular hyperplasia).  Thallium scintigraphy was shown to have high accuracy (92%) in detecting breast cancer, better than mammography (74%) and ultrasonography (84%).  Almost all (51/56) breast cancers showed greater 201Tl activity than surrounding normal breast tissue while there was no significant increase in 201Tl activity above background in all but one (19/20) case of non-malignant disease.  201Tl activity within breast tumours, calculated as tumour/background (T/B) ratio, ranged between 1.2 and 2.5 with a mean value of 1.45.  In our experience the concentration of thallium in the breast cancer seems to be primarily dependent on vascularity and tumour size rather than tumour grading, lymphatic/vascular invasion or receptor status.  201Tl scan sensitivity was 97% for malignant lesions larger than 1.5 cm (n = 35) and 80% for lesions of 1.5 cm or less (n = 21); however, five of the eight breast cancers smaller than 1.0 cm were also detectable by 201Tl scintigraphy, compared with five out of seven by mammography.  Thallium scintigraphy would not be useful in evaluating the axilla for lymph node metastases (sensitivity 27%, specificity 77%).