목적: Dedifferentiation of metastatic papillary thyroid carcinoma(PTC) was thought to ascribe resistance to radioactive iodine treatment(RAI). To provide a reference regarding the status of dedifferentiation and genetic mutation, we investigated the expression of differentiation markers and BRAF-V600E mutation of PTC in matched sample of patients with lateral neck metastasis at initial diagnosis. 방법:Among 269 consecutive patients who received total thyroidectomy in conjunction with therapeutic central or lateral neck dissection for clinically N1b PTC from Oct 2005 to Jan 2011, 22 women were included. Direct sequencing and peptide nucleic acid (PNA)-mediated clamping PCR for BRAF-V600E mutation as well as immunohistochemical staining(IHC) of sodium-iodide symporter(NIS), thyroglobulin(Tg), thyroxin peroxidase(TPO) and thyroid stimulating hormone recepter(TSHR) were performed in thyroid tumor and central(CNM) or lateral neck lymph node metastasis(LNM). To quantify expression of differentiation markers, Aperio Image Scope morphometry was used. 결과:BRAFV600E mutation showed united results in 15(68.2%) patients, however, 7 (31.8%) patients showed different results according to the lesions. Expression of NIS, TPO and TSHR were not different among lesions. Expression of Tg in CNM was significantly higher than thyroid (p = 0.033) and LNM(p = 0.038). The expression of all markers were not different according to BRAF-V600E mutation, however, was significantly lower in patients who showed regional recurrence after RAI. 결론:The presence of BRAFV600E were observed with high frequency in PTC and metastatic lymph nodes. However, they could show different results in some patients. Expression of differentiation markers were maintained along the sequential metastasis in advanced PTC presenting lateral neck metastasis at initial diagnosis and can be lower in recurred patients.