DYNAMIC IMAGING - SCINTIMAMMOGRAPHY

Although mammography remains the technique of choice for the early det ection of breast cancer, new emerging breast imaging techniques such a s ultrasound, magnetic resonance and radionuclide scanning have been i nvestigated and included in many diagnostic protocols. This overview d iscusses the current problems related to radionuclide breast imaging t rying to define its role in the management of women with suspicious br east lesions at mammography. A number of tumor-imaging agents have bee n recently used for the differential diagnosis of malignant and benign lesions in radiographically dense breasts and breasts with architectu ral distortions from prior biopsy or surgery or following radiation th erapy. Tc-99m-MIBI is the most used tracer which has become the paradi gm of this new class of compounds suitable for breast imaging. The cur rent sensitivity and specificity rates for breast scintigraphy with Tc -99m-MIBI depend on a number of factors including lesion size and site . Sensitivity and specificity rates and positive and negative predicti ve values of 92, 89, 81 and 96%, respectively, have been reported in a large series of patients with palpable breast lesions, which figures have been confirmed in many other series. On the contrary, lower sensi tivity has been reported for nonpalpable breast abnormalities or for l esions smaller than 1 cm. This observation, confirmed by many authors, implies that a new nonpalpable lesion that is suspicious for malignan cy at mammography needs a histologic diagnosis. We also report the res ults of our recent studies on functional imaging with Tc-99m-MIBI of t he multidrug resistance phenotype in breast cancer patients. These stu dies followed an observation that this tracer is a suitable transport substrate for the P-glycoprotein (P-gp) which is commonly associated w ith the development of a multidrug resistance phenotype. We examined 3 0 patients with histologically confirmed breast carcinoma who had rece ived no previous chemotherapy or preoperative local irradiation. We fo und a positive and significant correlation between the efflux rates of Tc-99m-MIBI determined by in vivo kinetic analysis and the P-gp level s measured in vitro by quantitative autoradiography in the same tumors (r = 0.62; p < 0.001). More recently, we tested whether tumor clearan ce of Tc-99m-MIBI can predict the response to neoadjuvant chemotherapy in patients with locally advanced breast cancer. Thirty-nine patients with stage III disease underwent Tc-99m-MIBI scanning before neoadjuv ant chemotherapy and the time to half-clearance of the tracer was calc ulated. The patients then received epirubicin and underwent mastectomy after completing chemotherapy. This study showed that a rapid tumor c learance of Tc-99m-MIBI (less than or equal to 204 min) can predict th e lack of tumor response to neoadjuvant chemotherapy with drugs affect ed by multidrug resistance phenotype in advanced breast carcinoma pati ents. However, slower tracer clearance (greater than or equal to 204 m in) did not guarantee an objective tumor response to chemotherapy in a ll patients, in agreement with the existence of several P-gp-independe nt mechanisms of drug resistance. We conclude that the preliminary stu dy of this phenotype would allow to predict the response to (neo)adjuv ant chemotherapy and select the appropriate treatment regimen for each patient. Finally, radionuclide breast scanning may be helpful in the differential diagnosis of malignant and benign breast lesions as a gui de to subsequent chemotherapy. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.