Tc-99m-MIBI scintigraphy as an indicator of the chemosensitivity of anthracyclines in patients with breast cancer

Background: Chemoresistance of tumor cells is involved with many factors, o ne of which is the P-glycoprotein function to pump anthracyclines out of ce lls. Tc-99m-MIBI accumulates in several tumors, and some of these cells was h out Tc-99m-MIBI through P-glycoprotein. Materials and Methods: We investi gated if the wash-out of Tc-99m-MIBI from the tumor in fifteen female patie nts with breast cancer could be related with the chemosensitivity of antica ncer agents; doxorubicin (DOX), epirubicin (FAM), pinorubicin (PINO), mitom ycin (MMC), cisplatin (CDDP), and 5-fluorouracil (5-FU), in each tumor tiss ues. The wash-out of Tc-99m-MIBI, defined as retention index, was quantifie d from an early and delayed Tc-99m-MIBI imaging. The chemosensitivity of th e anticancer agent, and inhibition ratio, was determined in vitro assay by using surgical specimens obtained from patients who underwent Tc-99m-MIBI i maging. P-glycoprotein in the surgical specimen was studied by immunohistoc hemical staining on its paraffin section using a monoclonal antibody. Resul ts: Inhibition ratio of anthracycline agent, DOX, FAM and PINO, was well co rrelated with retention index of Tc-99m-MIBI with coefficient of 0.75, 0.60 , or 0.62, respectively, whereas a poor relationship was observed for MMC a nd CDDP. The retention indices of Tc-99m-MIBI were remarkably small for pat ients in the P-glycoprotein positive group. Conclusion: Tc-99m-MIBI retenti on index quantified from its early and delayed scintigraphy is a good indic ator to predict the chemosensitivity of anthracyclines in untreated breast cancer.