PRIMARY BREAST-CANCER IMAGING WITH TC-99M SESTAMIBI AND ITS RELATION WITH P-GLYCOPROTEIN OVEREXPRESSION

The aim of this preliminary study was to evaluate retrospectively sest amibi scintigraphy in relation to the presence of the 170-kDa P-glycop rotein (Pgp), which represents an expression of multidrug resistance i n patients with primary breast cancer, Fifteen women (age range 37-76 years) were referred for technetium-99m sestamibi scintigraphy because of suspicious breast lesions detected by mammography and ultrasonogra phy, and subsequently assessed by fine-needle aspiration. Scintigraphy was performed 30 min following the injection of 500 MBq Tc-99m-sestam ibi. Three planar anterior and oblique images were obtained with the p atient in the supine position. Excised tumours were assessed for cytos olic CA 15.3, oestrogen (OR) and progesterone (PR) receptors and c-erb B2 neu oncogene. Pathology revealed that only 13 of the 15 patients h ad malignant rumours. The two benign tumours were sestamibi-negative a nd Pgp-positive. Sestamibi scintigraphy was positive in 10 of the 13 m alignant lesions (including nine of ten infiltrating ductal carcinomas ). Two of the three lesions with false-negative scintigraphy were Pgp- negative; in one of these cases histology revealed an invasive lobular carcinoma and in the other, mucinous adenocarcinoma. The third false- negative lesion was a Pgp-positive infiltrating ductal carcinoma which was c-erb B2 neu-negative but CA 15.3-, OR- and PR-positive. This pre liminary study confirms that the resistance to chemotherapy which may occur in patients with primary breast cancer can be a cause of negativ e sestamibi scintigraphy.