99mTc-MIBI scintigraphy in metastatic renal cell carcinoma: clinical validation of the relationship between 99mTc-MIBI uptake and P-glycoprotein expression in tumour tissue.

Technetium-99m hexakis-2-methoxyisobutylisonitrile (MIBI) and thallium-201 imaging was performed in a patient with metastatic renal cell carcinoma (RCC), which is a well-known tumour type demonstrating P1-glycoprotein (PGP) overexpression. Two scintigraphic patterns - Tl(+)/MIBI(-) in primary tumour and Tl(+)/MIBI(+) in metastatic tumour - were observed, suggesting high- and low-level PGP expression, respectively. Immunochemical study for PGP revealed strong staining of the primary tumour cells. This case clinically validates the previously suggested relationship between 99mTc-MIBI uptake and PGP expression.