Expression of sodium-iodide symporter and TSH receptor in subclinical metastatic lymph nodes of papillary thyroid microcarcinoma

Background. The clinical significance of the subclinical lymph node (LN) metastasis in clinically node-negative (cN0) papillary thyroid microcarcinoma (PTMC) has been debated. We investigated the expression of sodium-iodide symporter (NIS) and thyroid-stimulating hormone receptor (TSHR) in the subclinical metastatic LNs of PTMC, which are crucial prerequisites for the response to radioactive iodine treatment. Methods. Among 149 consecutive patients who received total thyroidectomy in conjunction with prophylactic central neck dissection for cN0 PTMC from October 2005 to December 2007, 20 who had single PTMC and subclinical LN metastasis (cN0, pN1, single PTMC) were included. Immunohistochemical staining was performed with antihuman NIS antibody and anti-human TSHR antibody in 20 primary tumors and 52 metastatic LNs. Results. NIS and TSHR expression was detected in 19 (95%) and 18 (90%) of 20 PTMCs, respectively. NIS and TSHR expression were also detected in 50 (96.2%) and 39 (75%) of 52 metastatic LNs, respectively. In 85% of patients, the presence of NIS expression in primary PTMCs was concordant with that in corresponding metastatic LNs. Intensities of NIS and TSHR expression were diverse. In 6 of 12 cases of multiple metastatic LNs, the metastatic LNs showed heterogeneous intensities of NIS expression. Conclusions. The presence of NIS and TSHR expression was observed with high frequency in both PTMCs and corresponding subclinical metastatic LNs. However, the intensity of NIS and TSHR expression was diverse. Multiple metastatic LNs from single primary tumor focus could have heterogeneous intensity of NIS expression.