Thisin vitro method provides information on the potential to inhibit the active transport of extracellular iodide across the cellular membrane. It employs the SK reaction on the MCF7hNIS breast cancer cell line that overexpresses the human sodium iodine symporter (NIS). Similar results have been observed with this cell line as compared to the HEK293 hNIS cell line from the US-EPA. Here, SLC5A5 is linked to breast cancer.