Clinical validation of the influence of P-glycoprotein on technetium-99m-sestamibi uptake in malignant tumors

We prospectively studied 48 patients with either breast cancer (30 patients) or lung cancer (18 patients) to ascertain the relationship between the degree of accumulation of ^99mTc-sestamibi and the expression of p-glycoprotein in tumor tissues. Methods: During initial presentation (37 patients) or post-therapy evaluation (11 patients), the patients underwent contemporaneous ^99mTc-sestamibi imaging and biopsy (30 patients) or surgery (18 patients). The interval between surgery/biopsy and imaging varied between 3 and 15 days. All patients had radiologically detectable tumors. Immuno-histochemical studies were performed on paraffin sections using a monoclonal antibody, JSB-1, developed against the internal epitope of p-glycoprotein. Tumor-to-background ratios were correlated with the level of p-glycoprotein expression determined by immunohistochemical studies. Results: Our results showed an inverse correlation between the tumor-to-background ratios of ^99mTc-sestamibi and the density of p-glycoprotein expression in tumor tissues. The values for the tumor-to-background ratios were significantly lower for those tumors expressing p-glycoprotein at high levels than those with scattered and no expression (p < 0.01 and p < 0.001, respectively). Conclusion: Although our results warrant further studies at the molecular level using PCR techniques after the extraction of mRNA, our data strongly suggest that ^99mTc-sestamibi imaging is useful to noninvasively determine the presence of multidrug resistance in patients with malignant tumors.