99mTcO4- accumulation in scintigraphy and expression of Na+/I- symporter in salivary gland tumors.

Abstract

Warthin's tumors and oncocytomas show exceptionally good (99m)TcO4(-) (Tc) accumulation images in Tc scintigraphy. However, the mechanism of Tc accumulation in these tumors remains unclear. Sodium-iodide symporter (NIS) is a plasma membrane protein expressed in the thyroid, lactating breast, stomach and salivary glands; it facilitates uptake of I(-) and Tc. We hypothesized that Warthin's tumor cells and oncocytomas may also express NIS, which would promote uptake of Tc. We examined NIS localization and the mechanism of Tc accumulation in various salivary gland tissues. Immunohistological localization of NIS was performed for 19 tumors from 18 patients who underwent preoperative Tc scintigraphy. Expression of mRNA for NIS in the normal salivary gland, Warthin's tumors and pleomorphic adenomas was analyzed by real-time PCR. In normal salivary glands, striated duct cells were strongly immunostained by anti-NIS antibodies. In Warthin's tumors, eosinophilic epithelial cells exhibited positive immunostaining, but their staining was varied among the cases. Furthermore, all Tc-positive specimens were NIS-positive, and all Tc-negative specimens were NIS-negative. Real-time PCR showed that NIS mRNA expression was detectable in normal salivary glands and Warthin's tumor cells. The expression was significantly higher in normal salivary glands compared with Warthin's tumor cells and pleomorphic adenoma. Tc-positive salivary glands expressed NIS. Our findings suggest that Tc accumulation in Warthin's tumors and oncocytomas is due to poorer Tc excretory function compared with normal salivary gland tissues, in addition to active uptake of (99m)TcO4(-) via NIS.