Expression of sodium iodide symporter in human breast tissues.

Purpose: Sodium iodide symporter (NIS) expression in breast cancer (BC) tissues suggests the possibility of using radioiodine for diagnostic and therapeutic purposes. This study evaluated NIS protein expression in primary BC samples and its association with BC prognostic markers and thyroid functional parameters. Methods: Fifty-six breast tissue samples from 52 operated women (41 BC, 11 benign breast diseases (BBD) and 4 peritumoral adjacent to the carcinoma tissues samples) were analyzed by immunohistochemistry using monoclonal anti-NIS antibody. Measurements of baseline levels of thyroid hormones and antibodies were also analysed in association with NIS protein expression. Results: NIS presented positive cytoplasmic immunoreactivity in the majority of BBD samples (45%) and in 3 out of 4 breast tissues adjacent to carcinoma. Immunoreactivity was extremely faint in BC samples. Mean thyroid hormones levels and thyroid antibodies positivity did not differ statistically between patients with NIS positive (faint expression) and NIS negative BC. NIS expression appeared to be independent of estrogen (ER) and progesterone receptor (PR) expression as well as of lymph node status. Conclusions: BC samples expressed only faintly and mainly cytoplasmic NIS protein, suggesting the presence of a non-functional NIS protein. The hypothesis of the down regulation of NIS expression during carcinogenesis cannot be excluded.