Size and P-glycoprotein expression limit 99mTc-tetrofosmin uptake in parathyroid adenomas

The purpose of this study was to retrospectively evaluate (99m)Tc-tetrofosmin (Tc-TF) uptake in large parathyroid adenomas and to compare the results with their expression of multidrug resistance (MDR)-mediated, 170 kDa, P-glycoprotein (Pgp). Twenty patients with large parathyroid adenomas (larger than 1.5 g), who had undergone early and delayed (10 min and 2 h) Tc-TF parathyroid imaging before operation, were enrolled in this retrospective study. Immunohistochemical analyses were performed on multiple, non-consecutive sections of the 20 parathyroid adenomas and 40 normal control specimens (20 normal parathyroid glands and 16 normal thyroid specimens) to detect Pgp expression. Tc-TF parathyroid imaging accurately localized 17 large parathyroid adenomas, but not the remaining three. The 17 parathyroid adenomas with significant Tc-TF uptake in delayed (2 h) parathyroid images revealed negative Pgp expression, but the three adenomas without significant Tc-TF uptake, as well as 20 normal parathyroid glands and 20 normal thyroid specimens, revealed positive Pgp expression. Therefore, not only the size, but also the expression of Pgp, limited the sensitivity of Tc-TF parathyroid imaging to localize parathyroid adenomas before operation.