P-Glycoprotein and multidrug resistance-related protein expressions in relation to technetium-99m methoxyisobutylisonitrile scintimammography findings.

The purpose of this study was to retrospectively study 48 patients with infiltrating ductal breast cancer to evaluate the relationship between the degree of accumulation of technetium-99m methoxyisobutylisonitrile (Tc-MIBI) and P-glycoprotein (Pgp) or multidrug resistance-related protein (MRP) expression in breast cancer tissues. Before surgery or biopsy, all 48 patients underwent scintimammography started 10 min after the injection of Tc-MIBI. Tumor:background (T:B) ratios were calculated from the Tc-MIBI scintimammography. Immunohistochemical analysis was performed on the pathological specimens of the 48 breast tumors to determine Pgp and MRP expression. According to the results of immunohistochemical analysis, the 48 breast cancers were separated into four groups: (a) group 1, 12 cancers with both positive Pgp expression and positive MRP expression; (b) group 2, 12 cancers with positive Pgp expression and negative MRP expression; (c) group 3, 12 cancers with negative Pgp expression and positive MRP expression; and (d) group 4, 12 cancers with both negative Pgp expression and negative MRP expression. Among the four groups, the T:B ratio was lowest in group 1 (1.13+/-0.10) and highest in group 4 (2.17+/-0.14), respectively (P < 0.05). The T:B ratios of groups 2 (1.30+/-0.25) and 3 (1.32+/-0.26) were between those of groups 1 and 4. Our data confirmed that Tc-MIBI scintimammography is useful for determining Pgp and MRP expression in patients with breast cancers.