The Na+/I− Symporter Mediates Iodide Uptake in Breast Cancer Metastases and Can Be Selectively Down-Regulated in the Thyroid

Abstract
Purpose: The Na+/I symporter (NIS) is a key plasma membrane protein that mediates active iodide (I) transport in the thyroid, lactating breast, and other tissues. Functional NIS expression in thyroid cancer accounts for the longstanding success of radioactive iodide (131I) ablation of metastases after thyroidectomy. Breast cancer is the only other cancer demonstrating endogenous functional NIS expression. Until now, NIS activity in breast cancer metastases (BCM) was unproven.