99mTc MIBI prone scintimammography (PSM) is reported to be a specific examination in order to assess the nature of breast lesions. Fifty-three patients whose mammography was stratified according to the breast imaging reporting and data system (BI-RADS), the five category classification of mammography approved by the American college of radiology, were studied with prone scintimammography, with the aim of assessing the accuracy of this exam and its usefulness in clinical practice. Thirty-five out of forty-one patients with BI-RADS category V (high probability of cancer) showed cancer at histology. Thirty-one of them had positive PSM. Three out of the six patients with mammo-graphic features of category IV indicated malignancy. PSM was positive in all of them and negative in the three benign lesions. One of the five patients with category III mammography showed cancer and positive PSM. The PSM was negative in 12/13 patients with benign patology (specificity 92.3%). When the cancers were stratified for T-category significant differences were found between the sensitivity for tumors larger or smaller than 1 cm. The sensitivity was 50% for the cancers smaller than 1 cm and 96.9% for those larger than 1 cm. PSM is a very specific method to determine the nature of breast lesions. Its sensitivity is also high but has to be improved when tumors smaller than 1 cm have to be detected. From a clinical point of view PSM can at the moment be considered as an accurate method for the study of borderline lesions of IV and also of III BI-RADS category. In this case a positive PSM indicates an impact in clinical decision making.

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