Reduced or absent NA+/I- symporter expression in papillary thyroid microcarcinomas

Background Radioactive iodine (RAI) is a treatment for patients with thyroid carcinoma after thyroidectomy. The Na+/I- symporter (NIS) plays a role in this ability to concentrate iodide within tumor cells. Recent studies have shown a correlation between immunohistochemical staining of NIS and the ability to concentrate iodide mainly in tumors > 1.0 cm. Here only papillary thyroid microcarcinomas (PTMC) with or without LN metastasis (LNM) are evaluated to observe NIS expression. Design A retrospective study involved 47 cases of PTMC (24 with and 23 without LNM). Immunostains were performed using two different monoclonal anti-NIS antibodies: clone SPM186 from Abeam and clone FP5A from Millipore. Results The findings were very similar using two different monoclonal antibodies. One out of 24 cases with LNM displayed focal expression of NIS while two cases showed several NIS-positive cells. None of 23 cases without LNM and none of metastatic tumors showed NIS expression. Ten benign nodules with Hiirthle cell features exhibited moderate membranous stain. Conclusion PTMC with or without LNM show minimal to no expression of NIS. NIS expression and function may not be the same in PTMC vs a non-PTMC and RAI therapy may not be effective in treating PTMC due to lack of NIS.