Background: Chemoresistance of tumor cells is involved with many factors, one of which is the P-glycoprotein function to pump anthracyclines out of cells. 99mTc-MIBI accumulates in several tumors, and some of these cells wash out 99mTc-MIBI through P-glycoprotein.
Materials and methods: We investigated if the wash-out of 99mTc-MIBI from the tumor in fifteen female patients with breast cancer could be related with the chemosensitivity of anticancer agents; doxorubicin (DOX), epirubicin (FAM), pinorubicin (PINO), mitomycin (MMC), cisplatin (CDDP), and 5-fluorouracil (5-FU), in each tumor tissues. The wash-out of 99mTc-MIBI, defined as retention index, was quantified from an early and delayed 99mTc-MIBI imaging. The chemosensitivity of the anticancer agent, and inhibition ratio, was determined in vitro assay by using surgical specimens obtained from patients who underwent 99mTc-MIBI imaging. P-glycoprotein in the surgical specimen was studied by immunohistochemical staining on its paraffin section using a monoclonal antibody.
Results: Inhibition ratio of anthracycline agent, DOX, FAM or PINO, was well correlated with retention index of 99mTc-MIBI with coefficient of 0.75, 0.60, or 0.62, respectively, whereas a poor relationship was observed for MMC and CDDP. The retention indices of 99mTc-MIBI were remarkably small for patients in the P-glycoprotein positive group.
Conclusion: 99mTc-MIBI retention index quantified from its early and delayed scintigraphy is a good indicator to predict the chemosensitivity of anthracyclines in untreated breast cancer.