NIS Mediates Iodide Uptake in the Female Reproductive Tract and Is a Poor Prognostic Factor in Ovarian Cancer

Context: The sodium iodide symporter (NIS) mediates active transport of iodide into the thyroid and the lactating mammary glands and is highly expressed in thyroid and breast carcinomas. NIS is clinically very relevant because it allows the treatment with radioiodine of thyroid cancer patients. Objective: In this study we wanted to explore whether NIS is expressed in the ovary and in ovarian cancer. Methods/Patients: Methods included NIS and paired box 8 expression and function in ovarian cancer patients and rats by immunochemistry, immunoblot, RT-PCR, and iodide uptake. Results: Here we demonstrate for the first time that NIS is expressed in the ovary and fallopian tube and actively accumulates significant levels of radioiodide in vivo. In a large survey of menstruating women receiving radioiodide for medical purposes, 15% showed significant uptake in the normal reproductive tract. Ovarian NIS activity is influenced by the estrous cycle stage in rats, being up-regulated during peak levels of estrogens occurring immediately before the ovulation. We unveil that the regulatory mechanism underlying this phenomenon is based on the functional cooperation of estrogen receptor-alpha and paired box 8. We also show that NIS is highly expressed in ovarian cancer, predicting a poor prognosis in these patients. Conclusions: These results provide the basis that will help minimize the impact of therapeutic doses of radioiodide on gonadal function. We also suggest that NIS is a new ovarian cancer marker, opening a door for the use of radioiodide in the diagnosis and treatment of ovarian cancer patients.